Companion parties are very expensive as well--I don't recommend raising them until you're ready go independent and fight lots of consecutive battles to make up the cost. They're very good, but this is a long term tactic, not a short term one.
I generally do the same; avoid anybody that could beat me and try to target the weak lol. It's strategic common sense, and sometimes I lose despite that
. My favorite defeat being against King Edurand of Vlandia (he took over for his father during the first year of my playthrough and remained king for around 30 years) who basically showed me why Banner Knights and Sharpshooters are forces to be feared; the former are great at shock attacks while the latter deadly at range and will form circles of DEATH to smite anybody who dares approach them lol. I may have won the rematch (as my daughter/next generation), but that initial defeat against an army I outnumbered by a couple hundred really marked him as my rival during my warlord days lol.
Well, workshops are kinda like that; they often give nothing on some days and give a couple hundred on others. The best ones are generally near major trade centers, so Husn Fulq probably isn't the best, but you're experiencing my normal issue with them. Still, they pay for themselves in the long run, but you can't count on them in the short term.
You can't level them up to my knowledge; that may or may not be an unfinished mechanic. Workshops (and the economy in general) is in continuous development, so Workshops actually used to be more profitable a long time ago (from what I've read--I'm a newbie who started last December, y'know) before being massively nerfed (profits capped at 100 per day per workshop) and then buffed again before some economic restructuring since there was a time where price indexes were ridiculously low after a while. Now? Well, price indexes tend to increase over time--basically simualted inflation, which is good for counteracting troop wages since they're stagnant despite inflation--but workshops are very iffy.
Caravans are much better, but there's only two safe times to use them; during the time before you're a noble/ruler, and when you rule over a safe corner that nobody wants to declare war on (which actually happened to me; I had several years of peace while ruling the Nahasa Desert since nobody wanted to fight me due to being busy with others. What wars we did eventually fight were ones I rubber-stamped lol).
Speaking of rubber-stamps and promoting companions; you need, if I recall correctly, some number of influence (50? 200?) plus 25 or 50,000 denars (I can't remember off-hand, but it's not THAT expensive by the time you can do it) so you're going to be alone until you grind up Influence as a corner king. My advice would be to hang around your territory and grind your former allies for Influence since you don't need democratic approval to pass laws as a faction of one; so, just enact every desirable policy you can and THEN set about buying the loyalty of imprisoned clan heads and donating castles to a handful of favorite companions (ideally companions with high Steward, Leadership, Scout, and the like). If you set up your territories to be hard to attack (and conveniently declare presence while the Southern Empire's at war with, say, everybody...) then it can be a pretty "chill" phase of play, but it can also be insanely hectic if you do it too soon or too recklessly. It's really the make or break for your kingdom as a whole though, which is why I encourage going slow and steady while you're in a relatively cushy phase as a nobleman (granted, your bills might make you sweat a little, but you should be in the black if you factor money gained from selling loot and well on your way to expanding your territory).
I suspect Husn Fulq will be quite a nice place to set up shop; I'd definitely shoot west for Razih, but the castles near the Duzeg Steppe would be good for vassals as well, not to mention nice forward operating bases and decoys during your inevitable war of secession.