First off a few notes on your post, I'm assuming you're not a native speaker (if you are, please carefully read your post before posting), it's a bit hard to follow at points but I think I get the gist of it (if I'm wrong on anything relevant feel free to correct me and I might be able to give you a more useful answer). Also what you rolled on what dice is of no concern here and just distracts from what is important, which seems to be: you randomly determined your character's (I suppose it could also be someone else's, but I'll assume it's yours) background and got a crown prince masquerading as a (wealthy) commoner, you furthermore decided he'd be a mercenary leader. Nor is what a Warrior-mage is of any importance to your questions.
1: I'd expect very mixed, a group of people is comprised of a number of individuals, each with their own views. If your character is generally well liked by his followers most probably wouldn't mind too much, although they might be confused as to why you'd pretend to be a commoner. Others might suddenly go from liking your character well enough to hating him due to holding a grudge against your character's father/family (think Raven in Fire Emblem (GBA), if you've played that one). If your character isn't liked, or not particularly well, it's probably not going to help, but I'm not seeing any potential for great harm either.
2: If your character's father (at least somewhat) approves of the situation it could at least make sense (like Uther sending Oswin after Hector, again in Fire Emblem, who wasn't necessarily pretending to be a commoner but was running off to do something else than was expected of of an heir-apparent). Whether it's a good idea depends on what you're judging it on (like what do you want with it).
The last one is the least clear of the questions, which is a shame, as it's also the most interesting. I think you're asking: are there any crimes to watch out for that his mercenary band might commit? And if so, will a pardon save your character and his band from the repercussions? (Or possibly only the second one.)
3: It's important to realise that law in the middle ages (which most Fire Emblem settings seem to be based on) was very different from how we imagine law today, besides church law (which I'll ignore as most Fire Emblem settings don't seem to have a church nearly as influential as the Catholic Church was in Medieval Europe) there were customary law and whatever the local lord decided was law (and could enforce), neither of these are particularly predictable and can easily vary from region to region, as such the law is basically whatever the DM says it is (you could of course ask the DM about laws to be aware of, your character would probably know at least a good part of them). Although you should probably be fine if you just fight highwaymen, raiders and the like, but not so much if you decide to fight the local lord or his men (regardless of whether you're paid for it). Most current laws of war are quite modern so you probably wouldn't get in trouble for something like refusing a surrender (and that's ignoring the question of whether your enemies were lawful combatants, if you'd want to apply current laws of war).
As for whether a pardon would save you, that very much depends on who captures you and what you've done, as well as on the amount of power the king has over the kingdom.
If they're captured by whoever they were fighting, probably not, although depending on the circumstances a ransom (possibly called damages or something like that) might fix it.
Otherwise it'll depend on who and why. It's hard to give clear answers here but whoever captures you being friendly/loyal towards the king would work in your favor while being hostile/disloyal or on the verge of rebellion would work against you. Having fought against your captor might work quite strongly against you. Being captured in another country would add a whole lot of issues but mainly it would come down to the factors I mentioned (relations with your character's father and having fought against your captor or not).
Also interesting is that you may well be assumed to have been acting on the king's behalf, so if you're captured by a lord you've been fighting against not only may a pardon not save you but you'd also risk causing a revolt, as it could be seen as the king attacking one of his vassals unprovoked, or even a war if you're captured abroad.
