As many LNBf's as you can fit into the spaces that do not shadow or block any signals from the other lnbf's placed for the satellites you want.
The problems are at 2 degree's; where the two satellites you want are located next to each other in space. Directv feedhorn's (lnbf's for multi-sat; 99/101/103) used today, have a patent on formed material at 2 degree's; look at their feed; and it should be clearer.
Also, obstructions like buildings; tree's, etc. need to be planned for the installation and understood. All of the lnbf's also need exacting placement and statics rules (tight bolts, material does not move); as well as angle accrued to the satellite wanted needs to be prime focused to the center of the dish; and skew for each correct.
It needs a real pointed dish also; as the center focused lnbf and satellite it gets determines what other angles are available to the dish. The lnbf's follow the angles of the arc; instead of using a motor; but all the satellites available depend on the dish itself being installed for the rest.
What this means is that the bracket; dish; lnbf's; switch/switches; must be exact and correct; and really only a few people do it this way; because it is not easy to do without knowing the arc like a motor makes for your dish. Getting matched components for this type is only one brand right now that i can see (other than homemade designs used since the 70's in the cable industry).
And, the system with multi-lnbf's is way better for multi-receivers using dual lnbf's and multi-switches; making it better than having 4 motorized dishes.