Haha. I'm the same way. It's fun to tinker with that stuff. It's actually probably a good thing it's so expensive otherwise I'd have twice as many half finished renovations.

Just be sure you're aware of local laws. At least where I live home owners can do all of their own electrical work as long as they get it inspected but that isn't the case everywhere. As far as the minisplit goes you should be legal to DIY it as long as you use precharged units and linesets. You just can't buy refrigerants or legally tap into the system in any way unless you have an EPA 608 certification. But if you're using precharged linesets and the equipment works then you won't need to do either of those things unless you somehow lose the refrigerant charge. As far as the rest goes just do your research on system sizing, placement, and all that jazz. But as far as DIY goes, a minisplit is probably about the same difficulty level as installing a new gas furnace so if you would be comfortable doing that they you should be fine.

Also if you're going with a heat pump minisplit, I'd go with mitsubishi, not a samsung. The Samsung units are more technically advanced and have more flashy options but they aren't very reliable. I've worked on several that had major issues less than a year after install. They're also more "proprietary" when it comes to working on them. On the other hand I have never come across a dead mitsubishi with less than 5 years of hard use and they're dead simple to work on as far as minisplits go.