I don't think I'll track fills but I have wick, wire, build details/date and liquid.
That's what I have on my spreadsheet. Word table actually.
I keep 6 tanks going. 3 KFL's. One with 2 air holes, one with 1 air hole, and a mini. A Lemo, and a Lemo Drop. And a Nautilus. So they are all different and easy to identify. Used to have PT's going as well but I don't use them much any more.
I'm still figuring out what coils works best for me so having a record helps. Also reminds me when to replace wicks. I'm still not very good at telling when a wick is getting past its best. And some juices work better in particular tanks though I don't know why.
I used to have a bunch of different flavors, now it's just 4 regulars plus a couple I'm working on. Used to have a lot of tanks running too and never knew what coils or juice were in each. Doing it that way I never really knew what was working or how get it working better. Simple is good.
I decided to start donating my large collection of Spinners and PT minis to new vapers. I've given out 2 setups recently and both of them are doing well. I'll supply them with juice and heads for a while. I used to push smokers to change over. That never worked out. Now I wait until they come to me and ask.