Please help me understand some basics

Hey guys. i apologise in advance if this has been asked a million times or if theres a faq and i missed it. just have a couple questions to help me understand some basics. ive been stacking bitcoin for a while, now little bits here and there and putting it on to my cold wallet each time. i wasnt paying much attention when i forced got my wallet so basically:

1. I wrote my seedphrase when i got it but nothing else. was i meant to write down my private key or is that what the wallet is for?
2. speaking of private keys i have a seperate key for every single transaction ive made. from the $50 i put in the first time i got into bitcoin to the largest sum ive put in. is this normal or should i be 1 key?
3. A store opens up in my home town. it accepts bitcoin. i want to try it out cause i find it neat. do i carry my ledger with me and my seedphrase card to pay? doesnt seem right or safe. im not sure how do go about it.

im sure i have more but thats my main ones for now. i apologise again if these are common/annoying/noobish questions.