If you include all the addresses I had on various exchanges, I have probably used at least 250-300.
Well I didn't count my addresses on exchange sites because I don't consider them part of my wallet.
I suppose that's true since the address might be yours, but the wallet still belongs to the exchange. I would still technically consider them as my BTC addresses. Without them I would say I used roughly 100+ addresses.
You've got that right. It could be considered your address in exchange's wallet.