I believe the limit for one type of unit in space is 100. I don't know if mods can change that amount... You can have 100 mines, or 100 satalites, or 100 of both satalites and mines, but you can't have 200 sats.
Mods may change the amount of units per sector (either mines or satellites). The limit is per player incidentally, so three allies could theorically put 300 satellites/mines in the same sector.
You should also design a transport that is classed as a Troop Transport. The Troop Transport has a default strategy of capture planets. The regular transport has Don't get hurt.
I usually build my Troop transports with more armor and one or two planet wepons.
I think that if you put troops on a regular transport in strategic play the transport will run to a corner and never land the troops.