When dismounting units the valour doesn't change - a v0 mounted knight will dismount to a v0 foot knight even if it was trained in a v1 province for foot knights.

In XL (well certainly in v2, I've still not installed v3 yet....) the Crusade units are trainable by some factions - the Crusader states get ALL of them, including foot knights, and the Maltese Knights and Teutonic Order get their own respective units.

Other than this (and in Vanilla) crusader troops (Order Foot, various knights, and the less than overwhelming religious fanatics) will only be created IN a crusade stack once the crusade is launched. They will not appear anywhere else. You will not pick up any more en route - quite the opposite, they will desert just like other units, though maybe more slowly...

When a crusade passes through a province it can gain troops through two processes: it will suck some out of whatever army is there already, and it will recruit some from the "facilities", if zeal is high enough. I had played a long while before I'd noticed this second method when I realised that my crusade had picked up unit types that were not actually present in the province, but were trainable there.

Also crusade composition varies year to year. It doen't vary with destination - if you launch a crusade in say 1200AD, wherever you send it, it will start with the same troops. If you don't like the selection (ie all fanatics and no knight ) then reload and try next year. You may get a much better selection