In terms of bottles of ink, just three.
Waterman Serenity Blue - I brought this to be my baseline ink for new pens and nibs. The community seemed to view this ink as one of the few that will work in all pens regardless of their temperament so it seemed like a good option when starting out with a new pen for comparison against my others. Then I found out it is highly acidic. I think it eroded the plating along the edge of the slit on my matte black Pilot Vanishing Point and as two of my Sailors have an ion plated finish on the nib I have stopped using it.
Pilot Iroshizuku Ina-Ho - I brought this one simply because I I love the Iroshizuku line and liked the sample of Ina-Ho. They announced they were discontinuing it and I didn't want to find I couldn't get it in the future so I brought it - just in case. It is still sealed in its box! 😂
De Atramentis Document Black - I wanted a permanent ink for my bullet journal. I didn't want my year's calendar being wiped out by a spilled glass of water and this received good reviews and I liked the sample.
Otherwise I have a bit of a sample obsession. I mush have at least a hundred or more samples. Including the complete line of Iroshizuku inks, most of the De Atramentis Document inks, most of the Faber-Castel inks and large selections of Herbin and Diamine. Too many samples if I'm honest.
I feel my return to using fountain pens was a little over the top and moved faster than I could actually appreciate them. I started back into fountain pens in 2020 so I partially blame the pandemic for being over focused on a new hobby. This over the top progression included ink sample and notepad/paper purchasing. I was jumping from one pen/ink to another without forcing myself to spend the time to really get to know them. Ultimately, on top of other things I kind of burnt out on what felt like unnecessary stress of picking a pen and ink constantly and never feeling happy with it so wanting to swap to one of my others. It all ended up being packed away and I have just been using my Sailor Imperial Black multi-function ball point (the sacrilege of it!!!). Only just now am I getting ready to open the boxes again.
I hope to write a post about my experience at some point as an attempt to warn others about getting sucked in too quickly and missing the enjoyment of the experience of getting to know a new pen. I felt that the old fountain pen community kind of encouraged over consumption. I wish I had taken more time to explore my pens and inks.