I've already come to the conclusion that I want most of these silicon races to have been traveling in directions other than towards Earth, there being more resources closer to galactic center than at the rim, and the only reason humans got found at all is because a sleeper ship full of human colonists got intercepted as it was flying through the territory of one of these races. But I know very little in the way of being able to figure out distances and times and stuff. I do know that subjective time is less than the time of everyone else and so a journey of about 20-some lightyears is supposed to like only a few months to those in the ship. I've also decided that the sleeper ship gets intercepted quite a long ways away from what its eventual destination was to be.
So basically I just need to know how to figure out the relationship between subjective time and the real distance so I can decide where I want the different places to be in relation to each other. I'm also trying to figure out if there's a way for them to have radio communications with each other without SETI ever picking it up, even though they've been exploring space for millions of years.
Thanks in advance!