Ehm ..... a bit of reading may have given you most of the questions
Anyway ..... first, you can combine only a limited quantities of beams, due to the problems of the combination systems .....
As example, with a PBS (polarized beam splitter) you can easily combine 2 beams, one polarized in horizontal, one in vertical, so, 2 BR, or 2 red, or a BR and a red (that gives you magenta), but at this point, you cannot add other beams to this one using other polarizers ..... with dichros, it's the same, you can combine 2 different wavelenghts (one pass and one reflect), but not another same wavelenght beam with another dichro .....
With 2 dichros made for specific wavelenghts, you can combine 3 different wavelenghts ..... but if you have a beam that is already made with 2 wavelenghts, like cyan or magenta, the third one must be different, otherwise part of the combined beam become reflected away ..... and so on .....
Otherwise, you need special dichros, but i think they still have insane prices .....