Well, there's about a zillion different cultivars of Japanese maples (Acer palmatum) and they grow at different rates and to different sizes. To be any more specific, we would need to know what kind exactly :-)

And yes, they can be planted quite close to house foundations as they have very non-aggressive root systems. But precisely how close would again depend on what cultivars you are growing.

If no name provided at all and at that price, I would guess they are just species seedlings. But these are also very variable in growth rates and sizes but species trees tend to grow faster than the cultivars and in most cases, to rather large sizes - 20'+.

All it said on the pot was Acer Palmatum, so I'm thinking for the price, it's just the species acer palmatum.