The gap colonization and faction raids is quite significant: multiple in game years most of the time. Expect pirates to raid very soon after you've set up the colony though, so do have some cruisers ready, but main faction attacks take a long time to come. You need to have developed industries and be at size 5/6: even then, the typical attacks are pretty weak. If you want to, it is entirely viable to have a colony with just farming and pirate defenses to act as a home base/resupply point/income source and never deal with expeditions at all. Making your own ships however requires heavy industry, which will eventually attract expeditions.
Nex adds some depth in the form of agents that can adjust faction relations and do a few other neat things. It also adds random events that change relationships in extreme ways, up to and including major sections of the sector declaring war on you: this can be mitigated with agents, but requires babysitting and cash injections. If you want to play the conquest/faction relationship game with big mega fleets flying around, then Nex is fantastic. If you don't (which given this thread is about low tier early play forever I kind of think you don't) I highly recommend not using it.