On lowest settings, you get off with Goblin civ, Dwarven civ and Human/Elf civ. 3 civilizations in total on lowest settings smallest world. I know I play it. It doesn't help much with fps though. In 0.44.05, if you use "c"-ivilization interface and scroll over settlements you can see their population. Except your own settlement, for some reason known only to Toady.
On my embark I have goblin tower +200 population, my own fortress 110 pop, mountain home 0 civilized population and Human town +100 population. In locations you can set your restrictions for visitors. On my embark it took like one month, not even whole season, for a Human singer to show up, when I put in my first location in, which was tavern. However, I did build pretty extensive fortress by then like almost 20k quartz blocks and i had already quite few adamantine artifacts, worth like 1m each to back it up. I slapped "citizens only", as soon as I saw the visitor. After few years singer was still idling in my fort. Visiting guards of Human diplomat were constantly giving him beatings. Probably because he was nude. There was lots of blood each time and teeth. He wasn't leaving or applying for anything. Just idling in my general meeting area for ever. I just got tired and atom smashed him in my mass pit. I just see no point with visitors. Plus underground they get cave adaptation and above ground Dwarves refuse to clean. So it is just too huge harassment to keep visitors and try to keep fortress clean. DF is just bad with cleaning filth. Rain and bath do spawn entire new blood pools annoyingly, which is illogical. But this is not on topic now.
Make sure your fortress is worth few Dwarf bucks.
Make sure except your civilization and Goblin one, there is at least Elven or Human with some civilized population.
Wait a month.
However I have no idea, if there is some minimum population required for visitors too. I didn't see anything about that in init files.