Enigmatic Hat, what you want to do when you strike out on your own is have cultivated a lot of relations with nobles, especially in the faction you're planning on taking over but also in other factions. When you get into a fight with them (I think), you can ask them to instead switch over to your side, and if they like you enough, they will.
As for why you get caught, if you have a huge force and the dialog in the bottom left says "Your party has been spotted by [city/village/castle], that's why. If you've been spotted, you are pretty much guaranteed to get caught, and if you have a large party, you have a really high chance to be spotted.
I'd recommend you get Silverstag and start over, understanding stats. What I tend to do is have one or two party stats I, my character, levels up, take all the leader skills, and have companions take over different skills. Artimenner is good at siege work, Jeremus is good at medical, and Ymira is a good blank slate so I can make her do whatever I want. There are guides online, some mod-specific (I think Silverstag has one) about which companions hate which ones, so you can make sure you only get companions that like each other (and thus not have issues). You can also get a list of which companions dislike you sending out who for "Right to Rule" quests, and act accordingly, since if you send out who they hate before you send them out, they'll comment and say "You suck." and won't go out themselves. (I.E. if Jeremus hates Artimenner who hates Ymira who hates Rolf who hates Jeremus (These aren't the true ones, they're just names off my head) then if you don't have Rolf, you can send out Jeremus without any worry, then Artimenner (Jeremus will comment but since you already sent him out and can only send him once, there's nothing to worry about) then Ymira, and get as much RtR as you can manage~