Not sure it's tons - but it's enough to replace the full time job I quit.
Probably not the right way to do it, but it works for me!
I create what I love, in batches that seem balanced (some more feminine and some more masculine patterns, some tiny and some large, some seasonal) and I have some lines (like a line of local map themed items) that are wildly popular at shows.
I have several very large plastic drawer units and I know how many drawers I devote to each item. I sell mostly OOAK items locally so that people can find different items to entice them into my Etsy shop, and also so I can just go wild and enjoy creating whatever I feel like! So, for me, I have OOAK wood trinket boxes, and I know I need 3 full drawers. I know I need at least 2 dozen 9" map clips, which fit nicely into one deep drawer.
I'm very visual. Beginning of each week during show season I pull all the drawers, and make a quick list of what needs made. When I'm actually working on trinket boxes I pull those drawers and can quickly see if it looks like there aren't enough of a certain style for my liking. I keep them near me while working, so I can watch the collection til it looks like I want it to look.
I also use the PayHere reader (no promo for that reader - just what I started with) so I have a very easy way to track what sold at each show. I run even cash sales through it (no fees on cash sales) and I can see how many of each item sold each day, and even what sold each hour. I use that data to follow trends and plan for subsequent years.
Short answer on what I look for include:
~ very visual, so color and photos even are essential for me
~ ability to sort and track all data
~ no need for constant counting and inputting data
~ ability to keep separate inventories in one place. Drawer above each of the show drawers is drawer of inventory already made for my Etsy shop. In a pinch (busier show) I can pull from that Etsy inventory for a show.
Hope that helps *some*!