I haven't gone too far down the hole on a lot of gear. As I am fairly early on (barely in my second year?) so my biggest AD is probably just soaps.
I did buy a few cheaper razors I didn't like, and subsequently passed forward. No regrets there. Got to try a slant and an OC, which made the small price worth it.
Still the two Razors I have I am quite happy with (as of today, February 19... Lol). So if I started over, I'd still procure the Karve CB (A, B, C plates). I'd probably also want the Rockwell 6c as a backup / changeup from time to time. Oops, I also have a cheap Baili TTO for travel. I'd still buy one for that purpose. For $10, I'm not going to cry if a TSA agent absconds with it. Lol.
Brushes... I only have 5 now? Have 2 on order. So 7 is a good number. It's a full week rotation, provides variety, and plenty of backup as they die (hopefully years and years from now). I know for sure I like synthetic brushes... But I found that out immediately. I'm lucky, I guess.
Blades... I only have large amounts of the ones I really like. Even that is huge... 100-150 each max. I'm happy there. Ideally I like having a few hundred for safety sake.
Soaps... Ugh. I have bought a lot. Ditched some. If I knew then what I know now, I'd have gone softer here. Still, it has been (is still) a fun ride. So can I really complain? Nah. I'd nonetheless, tell myself to try samples, not whole tubs at first. Find my favorite type of soaps (fougere? Bay Rum? Fruit? Mentholated? Etc ). Then be more specific. Also have a limit.. maybe 10 max.