Starting a game before 100 or so can be boring, but your mountainhomes should be complete. I don't think it directly affects which civs have access to trade/attack you, but adventure mode would be miserably boring as you'd have one site per civ and nobody would know where to find any good beasts/bandits to kill.
But editing the raws IS easy.
Jsut go to your DFdirectory/raws/objects/creaturestandard.txt and find the kobold entry (just press ctrl-f and type 'kobold')
Then after the name, caste name, and child/child name tags write in [NO_EAT][NO_DRINK]
After that the kobolds will stop starving to death during world gen. Everything else can kill them as normal, however.
To actually check for and confirm you have kobolds in a world;
During world gen, immediately before 'accepting' the world, press p or whatever the option is. this will write a group of files to your main df directory by the number of the region and year. find regionX-world_sites_and_pops.txt, open it, and search for kobolds again. If it says nothing is there, the world has no surviving kobold population. If it does list kobolds, then they still exist. Throw a party during necessary pump stack construction and get magma'd.
You can export the information from legends mode as well.
After this you can go to legends, select the 'view historical maps' or whatever, press - or + until you find the most recent map and look around until you find a civ whose name is written in kobold gibberish. Mark or remember the location and embark within/near their territory. They should be there.
I'm trying to do this as well. I'm on the last step now.