Are there any mods out there that add brotherhood of steel and/or enclave patrols to the capitol wasteland? i have always thought that the presence of each faction was lacking, especially after the emergence of the enclave during the main quest

On nexus there are a couple:

BoS DC patrols - search on BoS
Marks Wasteland - more than just BoS - search mark

If you want regular travelers - MTC Travelers 2 - search on MTC

I always put them on the least amount of NPC settings - why - the wasteland can become extremely crowded and I don't think that you can call it a wasteland anymore. Some people like it that way. With more NPCs, Fallout 3 may become unstable and CTD. Luck.

how is marks wasteland for stability? It is my understanding that it makes changes to the main quest in order to apply these changes, My concern is that this could cause game breaking glitches or incompatibilities with other mods

Merc 2 is another to consider as it was just updated - I dont have Marks installed but considered it at one time....Outcast has it own patrols either by BS or FWE. Enclave comes in at the end. Good enough for me...MTC travellers I limit to the max cause I don't think lightly armed travellers should be out and about like armed patrols...