Right the first time isn't going to happen. There is no rule of thumb that will work. Generically speaking you want to bandpass your mid with a HP that allows it to play as low as possible for the listening levels and music you listen to. If it ever sounds stressed you need to raise it. The LP on the mid is a bit trickier as underlap, overlap, or the same cross point can all work depending on your installation locations and personal preferences. Typically as a rule of thumb you want to figure out how low your tweeter can play the same as with the mid, but you have to be much more careful as it is very easy to blow the tweeter. Once you have those ranges then you have to figure out when/where they mix the best. This could take many, many hours. Time alignment generically is used to compensate for path length differences. How to use it will depend on where your speakers are mounted, but usually you take the furthest away and adjust the rest to match.