I am right now in the process of starting my collection and in my head I am going through all of the bags I might possibly need and am trying to figure out what to buy. To acquire a nice collection, which I will get good use out of and not get tired of, I began to think about the things I ever carry with me. I thought about things I could ever do and need a handbag for. I thought about things I carry with me on a daily basis, things I carry to University, things I carry to work, things I carry when I run errands or go shopping. I have thought about the types of clothes I wear, I have considered that every once in a while I do have formal events, and I have considered the type of climate I live in.
I think it's good that you are putting some thought into what YOU want & need but don't rush to buy just to check off your list. Be aware that as your life changes, so will your needs. What you think you need now may not be true 10-20 yrs later.
My tastes in bags has change so many times over the decades. Some are repeated mistakes that I'm too embarrassed to mention or have been blocked completely from my mind until an odd picture surfaced with the bag in question.

Currently my categories are:
1. Every day bag: mid-sized leather bags with several options to carry. My current favorite is the LC cuir. Used to love BV montaigne until I found the corner wears too much to handle for a pricey bag. At least with the LC cuir, it won't break the bank to have multiples of. Being eyeing the Gucci Jackie but can't decide on a colour.
2. carefree nylon and leather bag/cross bodies: I have several styles in different price points. Used mostly when I travel or to some sport event. Currently like LC, Tumi, Prada and a couple of mid-low end names. A few are mementos from my travels shopping at local artisan markets. This category is probably my one weakness. Not because it cost the most but because I have so many and I like them all.
3. small leather bags: for weekend use or date nights with dh or friends. These are my pricier bags. My BBK is in this category.
4. Totes: mostly nylon or canvas. I have several of these and use them mostly as catch-all or carry-ons. Don't want to spend too much on them as they will get dirty from placing on ground, under seats or even used as foot rest for my kids.
5. evening clutches: satin or sequins. A few are inherited from my mom and the rest were purchased over the years to match the outfit. These are not expensive as I don't feel comfortable leaving $$$ bag on the table while I go dancing with dh or mingle with friends.
6. work bag: slim nylon laptop bag with compartments. Very boring black bag but I love it.
When I find that I know longer like or use the bag, I give it away or sell.