You can probably solo "easily" with good soloing classes up to about 6th level in the full game but in Unlimited I'm not entirely sure as I haven't taken a look at what adventures are available for free as some are packaged up in the micro payments side of things.
2 Races are store bought Warforged and Drow (although this can still be opened by favour points)
2 classes are store bought - Monk and Favoured Soul (although this can still be opened by favour points)
You can only have 2 characters, although you can buy more slots in the store
You start with a max of level 4, although sigils drop in level appropriate chests that expand this to 8,12,16,20 (Copper,Silver,Gold, Platinum Sigils) or you can buy them in store.
Hirelings - yes you can purchase hirelings which are one shot helpers, although they will follow you through a quest chain as long as you don't go back to the city in between etc.
It used to be that you could only have one hireling but I am sure I read that there is a way of filling your whole party out now. I'll have to test that as it may only be the DDO store hirelings that allow you to do that.
Jump onto Cannith the new server if you do as it's busy as hell and if you have an hour you should be able to PUG up quickly and get something done, or solo to your hearts content until mid-levels I would think.