In addition to getting payments going back to your application date, you can get up to 12 months of retroactive payments for the year prior to your application date (or your protective filing date, discussed below) -- if you were disabled that long ago.
Characters will receive one specialization point at level 7 and another at level 14. Specialization points can be saved for later levels or used mid-level (the Level Up button on the stats sheet will be active if there are unspent specialization points).
Like the other guild quest chains, the Thieves Guild quest chain will give you a new main quest in the chain when you rank up in the guild. So you'll likely need to get to rank 5 in the Thieves Guild skill line before you get the next quest. That won't be the case with you though, @Jcorv58. You must have missed one of the non-main quest story quests.