hot tub acquired--questions

i recently acquired a hot tub from a friend who had a divorce and had to get
rid of it.  I can't seem to figure out what brand of tub it is as there is
no markings/labels on it anywhere.  does this matter?

i don't know anything about it in terms of capacity, etc.  how can i ID this
tub?  don't i need to figure out how many gallons it is so that I can
purchase the correct heater and pump?  it came with a pump, timer and filter
but no heater.  how do i know what kind/size of heater to get for it?

any and all advice appreciated.

tb
austin, tx