[2] The best partner for product-selling sites like yours are Payment-processor Wallets like Coins Asia, Coinpayment or Bitpay (More: Google search results). It's up to you to research which is the best and legitimate among them.
Reason is: there are probably more mainstream consumers who use such service to buy things online, mostly all regular users have an account in those payment processors too (we use different type of wallets for different needs), that said, you wouldn't wanna miss the opportunity to reach that Market.

Examples of advantages of payment processors are instant payment (on the consumer's side), low to zero fees (again, on the consumer's side) and fool-proof apps which is why the mainstream prefer them over "real wallets".
Of course, P2P payment is still a-must in your payment options.

[3] Having 50+ available options IMO, is an overkill... Just pick the most legitimate coins and as much as possible, do not include tokens.