If you want to buy on ebay to resell then separate Buying and Selling accounts are a good idea.  You can have a store on your selling account so no need for another one there.

It is not a good idea to post on the boards with your Selling account but you could use your Buying account without too many worries about what might happen.

You can have as many accounts as you like but there are only the two that are really necessary....Buying and Selling and perhaps a Posting account.