No, it's not needed. It's designed in a way that you can have unlimited amounts of invader factions, but 1 works just as well.
Just set for all the invader factions you want (1, 2, 3, doesn't matter how many):
(faction_set_slot,"fac_*faction name*" ,slot_faction_invader_1,"trp_*first wave invader bot*"),
(faction_set_slot,"fac_*faction name*" ,slot_faction_invader_2,"trp_*5th wave invader bot*"), #New bots are introduced in the wave after the boss wave at wave no. 4
etc.etc.
Most likely you need to add some more challenge waves, as 6 and 10 are challengers, for example:
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_1,"trp_invader_challenge1"),
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_2,"trp_invader_challenge2"),
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_3,"trp_invader_challenge3"),
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_4,"trp_invader_challenge4"),
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_5,"trp_invader_challenge5"),
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_6,"trp_invader_challenge6"),
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_7,"trp_invader_challenge7"),
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_8,"trp_invader_challenge8"),
(faction_set_slot,"fac_invaders1" ,slot_faction_challenge_9,"trp_invader_challenge9"),