The "load ammount" command only comes into play, when you want your freighter-fleet to load several different installations.
Example: You have a 10-ship freighter fleet, with each freighter having 5 cargo holds and is thus able to carry a single mine/CF/...
You want to bring 5 mines, 3 CFs and 2 Ordnance factroies from earth to mars.
Then you need to order it to "load 5 x Mine", "Load 3 x Construction Factroy", "Load 2 x Ornance Factory"
If you only want to put Mines on Mars, the "Load Mines" and "Unload Mines" is enough
Note: Research Labs and Terraforming Installations are a lot larger than Mines/CFs, but will be brocken up and divided between several freighters and even several freighter runs.