Hmm, I may have been wrong about the ale - the game may mark it as a quest item that you can't sell. It's so long since I played vanilla, some things may only be possible in mods.
The only other vital mod I'd recommend would be the one that adds more siege ladders; you'll see how useful that will be shortly!
It's always the interesting part of the game where you get too big to chase bandits and too small to attack anyone else. You sometimes have to take risks at this point. You could always become a vassal and screw over that faction later. Alternatively you could stay on the periphery of an existing war and wait your chance - help or attack an army who have been disadvantaged in battle. Otherwise you could hone your troops into a lean fighting machine and chance it all on striking out as an independent warlord by attacking one of the factions yourself.
The Claimants stuff is up to you really, but it is essentially you fighting a war and then handing power to the claimant as your king. If you're going to go to all that trouble, why not just press your own claim? The most fun to be had with the game is in forming your own kingdom and trying to keep the others at bay!
The first thing you should do in battle is press F1 and F1 immediately (I think) to tell your troops to hold ground. Then ride out and figure out the enemy and then you can order different groups to do different things).
As for 'total conversion' mods, which are copies of the game but with a vast amount of features added, you need to look at those features listings and decide what works for you. Prophesy of Pendor is probably the most polished, and has tons of features, but it introduces fantasy elements. Native Expansion also has lots and lots of stuff that makes it a much more pleasurable game to play, but both it and PoP are much more difficult than Native. I also have to declare an interest in NE as I did a little work on it in the past. That's a while ago so it may not be one of the better mods any more. Check the feature lists.
Anyway, you have a bit to go before you start considering mods, I think.