That's really a personal choice in regards to your eBay accounts, one paypal account for both private and business is absolutely fine, however you can have one private and one business paypal account if you wish.
In regards to eBay accounts, the only downside to using one account to buy and sell is that your buyers can of course see what you, yourself buy by viewing your feedback as a buyer.
If that's not a big deal for you, then no issues at all. If you would prefer to keep that private, then a two account option would be applicable.
: )