3. Accounting: Legally accounting has to be on the official currency, so all buys/sell would have to be recorded in the legal currency and I guess in parallel in BTC to properly track the inventory, etc.[...] I understand held BTC won't pay any taxes but if eventually sold, I'll need the buy price of every sat to pay capital gains on that.
You can either use some block explorers that also record fiat value at the time of the transaction
[e.g. Blockchair] or simply use a cryptocurrency tax software
[e.g. Koinly (it's somewhat popular, but I prefer not to vouch so DYOR)].
5. AML/KYC: I'm going to be forced to perform AML/KYC check on clients. I don't see a workaround it. Also I'm not sure how to perform this in a timely manner during a regular shop transaction. I'm hoping this can be done "asynchronously"
This is going to have a detrimental effect on the number of potential customers who'd be coming to your brick-and-mortar shop... You can come up with a new platform that uses a KYC service from one of the known providers
[I prefer not to name any of them, but some of them quickly approve documents (if no flags are raised)].