Right now I'm focusing on a strength character, 24 strength (Because in Silverstag, the highest str-requiring armour is 24) and putting the rest into int and agility.
It's... REALLY great in sieges. I have this Balanced Knight Sword or something, that I can use with a shield on horseback and two-hand on the ground. One-hit kills most everyone, even lords (at least if I'm at speed on a horse) Add in the ability that gives you health regeneration for each kill, and it's almost imbalanced (I can still get over-whelmed though)
In terms of orders, I just keep my archers on a hill, the infantry a few paces in front of them, and tell them to hold fire until the enemy is in the valley of the hill. Especially if it's a lord fight, they might not actually move from there and stay in formation, soaking up tonnes of bolts. By that time, the enemy has spent all their arrows firing from a distance. (In Silverstag, there doesn't seem to be much cavalry, which is nice, when you get used to it. I haven't had more than 5 cav units on a fight, and most of those are companions)
As for Right to Rule and Opinion, 100 RTR is the maximum, so I guess 40 is good. If you want to send out your companions, make sure you do it in the right order (I think the Right to Rule wiki page has them) or else you'll get some companions refusing to go because you send out the person they "hate as emissary" already. You get 3 each, so if you have 9 or 10 companions (I think that's the max you can get of people who don't dislike other people in the party) that's 30 RtR right there. In Silverstag, I think importing/exporting companions is a little glitched, as I've had two people who in one game I fucked up and sent the person they hated, and then imported them into the next game, and they still go "Uh, yeah, right, I heard you wanna be king..." Hell, they even went into the whole "That bitch be cray-cray and so are you for supporting them!" in that game when I sent their hatemissary, even though they were already in the "Fuck you" mode.
As for opinion, 20 or 25 is usually what you need to get lords to start allowing you to visit their women (as a man-lord) and to start supporting you for marshal or to get fiefs.
And finally, to get people to follow you for sieges and such, you have two methods. One is to become marshal, in which case you talk to a lord and start a campaign, which should net you about 4 or 5 lords (if they start wandering ,which they might, just talk to them and say "I have a task for you: Follow me, you dumbass" and they should go "Yeah sure".
The other method is to get REALLY GOOD with them. I've never managed to get up in relations to the point where they'd follow you, they'd still say "I don't think that's proper, maybe you should follow me".
Finally, the factions are programmed so that they won't get wiped out without player intervention. I.e. the ai won't take the last castles of a faction unless you, as the player, lead the effort and take those castles yourself.