It's still possible to move 40,000 sat on-chain. Last time I paid 111 sat in fee.
If you receive those amounts, don't forget to
consolidate them before fees go up.
Will it limit sales to people who already own Bitcoin, or will buyers be prepared to purchase such a small amount?
I think it's pretty obvious you'll limit sales to Bitcoin owners if you only accept Bitcoin. I wouldn't buy a certain coin just because a one-time seller asks for it, I'd just find another seller.
Accepting LN would work, but has the same problem: only people who use it already will be able to buy from you.
You can check the withdrawal fee in Bitcoin with
Withdrawalfees.comBinance, Binance US charge the most expensive withdrawal fee.
Nice site, I sometimes use the #1 to convert an altcoin from a large exchange and get it back into Bitcoin (or LN directly). That route saves a lot of fees and makes much smaller withdrawals worthwhile.