Rules look pretty simple - though could use a bit more explanation. Looks like, roughly, 2.25 Chinese for each European legation force. Seems a bit low but must have worked out okay. A bit much with the division but, hey, that's why we have calculators. Buildings look good for the time you started collecting. Much nicer stuff available now but since the available reliable information is a little on the short side, who is to say what is right versus what isn't?
Working on my own Massive variation using the wonderful Bluemoon range of 15/18 mm buildings plus troops including the old Old Glory ranges and Cell Mate Miniatures figures (defunct) with some Lancashire figures. Already built a 12' long wall, just need to add the ramp and then its off to painting time.
Seems a very popular period. Good luck!