The exact plan is something that would be developed based on the political-economic situation that led to the revolution in the first leave and the needs that arose. There can be no perfect prescription because one cannot predict the exact situation we will inherit.

Immediately following revolution in the Russian Empire, the Bolsheviks had to fight a war against invading capitalist forces and domestic capitalist revanchists. They implemented forms of fatm collectivization that were largely restorative of traditional practice but without feudal lords and while also attempting to industrialize. This went less efficiently than needed so they adopted the NEP, then abandoned it for further central planning once its purpose was fulfilled. They ensured housing for all, placed doctors, cafes, and housing at factories, invested heavily in infrastructure and education, promoted women as part of the workforce and larger society against patriarchal attitudes, and prepared for the inevitable further invasion by capitalists, this time the fascists. They built based on their ability to control the means of production by and for those who work and based on the conditions they faced. They faced poverty, landlordism, a poor level of industrialization and infrastructure, joblessness, external military threats, etc. They implemented many policies over time attempting to work around hurdles, most of them imposed by capitalist countries trying to destroy them.

In China, they faced an even greater level of landlordism, of petty landowners that would routinely exercise inordinate control over people's lives and abuse them. China was even poorer than the Russian Empire, being a colonized country forced to subjugate its economy to foreign capitalusts. China had to fight a war against Japanese invaders and developed in the context of not just a liberatory nationalism but a betrayal of the communists by the KMT. They similarly had to industrialize, to deal with poverty, to deal with foreign aggression from capitalists that promptly encircled them and instituted sanctions. They achieved transformatiobs never before seen, of skyrocketing life expectancy, an end to famines, industrialization without stealing through colonialism.

When revolution comes to your country, what state will it be in? Will you have to kill neofascists that started a civil war? Will you need to rebuild a militant labor movement? Will there be an economic underclass most poised to contribute and then make demands of the transition?

Basically, when the working class has a liberatory victory, it can now more directly demand change. What changes will be a product of what is needed for the working class's own interests. In Cuba many villages had no doctor and essential medical care required a group of people to carry the sick for a day or more. So they built hospitals and trained doctors. They now have the best medical system in the world for a country with their size and wealth.

Anyways with that said I'll try to answer your specific questions.

Summer cottage?

lol who cares? A second home in a country full of homeless people!? I cannot be asked to care. Most likely it will be ignored because socialists are far too kind.

Family farm?

If you live in a rich, Western country these no longer exist. Farms are large agribusinesses owned by companies. Pappy had to sell his farm to them in the 70s and 80s.

What happens to pensions/retirement savings

These are numbers on a spreadsheet that are currently held by a bank or government. Their purpose is to guarantee retirement. During any real revolution the banks in question will be seized and repurposed, possibly even abolished depending on conditions, as they are the organ of society most antagonistic to us. There is no guarantee that the accounts will have anything in them nor that the government would have had any legitimacy to guarantee retirement before we won. They will try to take the money and run. They don't care about your pension, lol. It's just capital for them to lend out and make profits from.

Traditionally, socialists have simply guaranteed retirement via the state. An actual guarantee. And because socialists have also traditionally made so much of life available at no or low direct cost to the individual (housing, healthcare, transportation, food), this mostly just means you get to live your life exactly the same but just don't have to work.

land ownership

If the socialists are competent they will make the state the owner of all land and then figure out how to use previously corporate land for the public good and find a reasonable compromise on personal land. But it really depends on the conditions of revolution. Is land reform a revolutionary promise? What land and for what purpose?

inheritance

Should probably be largely abolushed but this also depends on the revolution. Nobody is coming for granny's keepsakes but you don't get to inherit the slave plantation.

small businesses

This is a term used for tax purposes in certain rich Western countries. It's not really meaningful for when to expropriate and plan, for example. Many industries should not even exist, they are parasitic, and this includes many small businesses. Smart socialists will not make decisions based solely on a tax bracket aside from needing to be practical about how to allocate transitions and planning resources. For example, China institutes more control over businesses as they become larger, both via government oversight and worker control.

the apartment your are renting out to pay for your own rent...

If you're doing that you're a financial idiot lol. Much better for the state to allocate your housing and keep you away from such decisions.

Socialists have traditionally guaranteed housing via various mechanisms, starting with building enough of it and ensuring it exists where people should be for economic activity. Connect it to transit, make it available bear industry and retail, etc.

Yeah, I know, these things tend to be out of reach for younger folks these days, precisely because of hyper wealth concentration.

Basically everything you mentioned is out of reach for the vast majority of humanity due to the capitalsti system. You're describing things that only the petite bourgeouis in impeeialist countries even think about. This us a very small number of privileged people even in those countries.

So with billionaires and mega corps out of the picture, the question still stands.

It doesn't stand at all, you are just unfamiliar with two centuries of working class political struggle and geopolitics. This is understandable, as Western educations do their very best to ignore most of it and misinform about the rest. One of the things they teach is the cartoonish impracticality of socialist systems that they describe with fanciful and false stories, basically fairy tales to appease reactionary capitalists that promote such propaganda in the first place and, for example, dictate what textbooks the Texas Board of Education buys and therefore the content in classrooms nationwide.

The untold reality is that socialists are actually very practical and realistic people that build from the needs of the wider working class and have traditionally tracked commodity prices and investments and military funding allocations and run and led worker revolrs and run and led wars of liberation. We are practical to a fault and endeavor to understand the world as it is and what is needed to liberate ourselves from an oppressive system and offer a vision of: what if we built this world for ourselves and not bankers or a noncorporeal profit-generating machine?