Yes, you can sell a character in the Character Bazaar and follow the rules. You will have to pay the transfer fee of €20 or 1000 PLEX (via GM, Support Ticket). It is possible that there may be some difficulties since your account is created by STEAM.
Any items that comes along with the DLC can be traded freely like any other items, but the GameTime applied to the account on purchase will not (this should be obvious).
I think you should consider to bypass STEAM altogether since there are some things that EVE’s Customer Support can’t help with because it’s through STEAM and their Customer Support are significantly more difficult to get help from.
I assume you’re talking about the Star + Galaxy packs: Can only be applied ONCE per account. I agree that saving 50% is a great deal but in all actuality you only get 1600 PLEX and 4 Multi char skill you can do with as you please.
Assuming that you are going to sell you characters from your previous accounts, you’d have to add the cost of that to the price of the items you plan to buy. so if you have more than 3 characters you “need” to sell you’d actually save more money by not buying the packs.
It is against EULA / rules to sell account. You will be banned if you try.
As ISD said, you can transfer or sell characters, but account remains yours, even if empty. Just write down details so you can remember the login later if you ever need, and ignore the empty account.
CCP may go through their database and delete empty accounts later. They’ll notify you if they do.