I think all my answers are yes.
Here is my very over simplified version or wholesale or dropshipping VS affiliate marketing.
In ans case, no one makes any money unless you do marketing, get traffic, have good copy and no how to convert (or in the case of affiliate marketing generate the click-through to the merchant.
So with wholesale or dropshipping if orders, customer service, support, cart issues and other stuff like that takes up 30% of your time, that's 30% less time you have to market and potentially 30% less sales.
To some degree it depends on where you like to spend your time, what you're good and where you want to focus your energy ie customer service, tech issues, order challenges, inventory OR marketing.
"Could I do both on the same site and make it seem seamless?"
Sure you could if you wanted to. But if it costs to get started,
is more work and not that much more profit, then why would you want to?
PS. I'm biased and affiliate marketing is what I do, so take that into consideration.