1) you don’t need a total station unless you are setting out / checking specific positions on complex geometry - which can still be done with distance and plumb etc. but takes far too long.
2) for a new build house etc. FFL will be dictated (usually) by the surrounding ground level, or a specific point that the roof level cannot go over etc.
For a datum, a solid fixed point that will not move, be dug up etc. a point in a road, pavement or concrete slab etc. is usual and you then give this a figure (can be Above Sea Level but not necessary unless there are multiple sites and locations working together, roads, bridges, shopping centres etc.)
Then use a dumpy level or water level from this point.
3) plan setting out is straightforward using tapes / large square / diagonal checking etc. - loads of YouTube stuff showing how to do it.