OK, too many people to answer directly so I'll just address the race questions with bullet points.

1. Majins: I'm afraid Dead Cruiser hit the nail on the head. The Androids wiped out Babidi when he tried to do his thing (since they were still around at the time, hell it could have easily happened while Trunks was in the past). Ergo, Buu is still in hibernation deep under the Earth (*cough*totallynotforshadowinganything*cough*), so there's no plausible way to use the Majin race.

2. Namek: Obviously Namek still exists, well sort of. Remember that vacation Goku took to New Namek where he saved them from Meta Cooler? Unfortunately, since Goku died in this timeline Meta Cooler succeeded in conquering New Namek and the Namekians are now either his slaves or scattered across the galaxy. Naturally, many of the ones who escaped would come to Earth, since it's the only other planet they know of. So yes, some Namekian refugees have started coming to Earth shortly after the Androids were destroyed.

3. Saiyans: This one should be pretty self-explanatory. Trunks is the only person in the [i]galaxy[/i] (note that I said "galaxy" and not "universe") with Saiyan blood. There are [i]technically[/i] three Saiyans still out there (Paragus, Broly, and Tarble) but I doubt any of them will be playing a role in this RP. That being said, Saiyans will have to be excluded from the list of playable races because, well, they're extinct, plain and simple. The fact that a couple of survivors are floating around in entirely different quadrants of the universe doesn't justify allowing a bunch of previously unknown survivors to start popping up for no reason.

4. Androids/Cyborgs: This one is... allowed, but do remember that Earth has just spent the last 20 or so years getting absolutely buttfucked by a pair of these, so good luck trying to survive the lynch mob that will absolutely no doubt be calling for your head should you go this route.