Rules of Thumb
An odd number of TUGs is good
Your army breaks on 50% of TUGs breaking, so an 11 TUG and a 12 TUG army both break on 6.
Competent Ally generals are alarmingly cheap and alarmingly likely to avoid joining in
Think about how many cards vs how many UGs you have.
An UG can't move without a card so if you have three competent commanders and 14 UGs then a lot of your army is likely to be sitting around doing nothing. That is not the end of the world if you have lots of missile weapons but it can be just a bit frustrating to have too few cards.
Try to consider how your army will operate when you pick your generals.
An army with four similar UGs that are likely to deploy and move together really needs a talented general to allow you to move 4 UGs as a group. Thinking about you generals and how you will use them in different situations against different opponents is important. For instance, if you might want to flank march a talented sub might be more valuable than a talented C-in-C. BE careful not to take mediocre in armies where the troops all want to be moving in blocks of 3 TuGs. But a mediocre with a specific role to take a TUG and a SuG together can be very effective. In short, don't treat your generals adn your troops as separate pruchases....
Small UGs are more fragile.
Losses are almost inevitable in MeG and a 4 base TUG or 6 base SUG that has lost a base is not too far from turning tail and running.
Allies need to have a specific job
An allied contingent only has one general, if you mix infantry and cavalry you are likely to end up with either the infantry or the cavalry in the wrong place, or out of command