Great guide. I'd like to share a little bit that I've picked up when searching for UA MRs. With some minor modification, these tips should be applicable to other airlines as well.

A trick I've found for making my MR's more comfortable is to use a range of flight numbers when searching in ITA. For example, using "UA1-1699+" searches for one or more flights that are only United mainline (excludes United Express flights and often therefore the smaller jets). When I'm getting a lot of results, it can help to cut the number down (and also provide some interesting routings).

This next bit of routing language is really useful when you're trying to use an ecert (to give an even better final CPM) and need all the flights to be on United metal. Instead of writing "UA+" to search for one or more UA flights, use "O:UA+". This searches for only UA metal flights (it excludes US-operated flights branded as a UA codeshare, etc).