Hi & welcome to HC
If you're new to hamsters then I would suggest just getting one hamster to begin with, having two can be quite a challenge, you need to be very careful about your cage set up to avoid territorial behaviour which can lead to fighting & most pairs do need separating once they mature & want there own space so it's not really that easy.
Hamsters live very happily alone, many will tend to bond with their owners better if they live alone too so there is quite a lot to consider before making your final decision.
I would advise having a second cage ready from the start though, dividing a cage seldom works well.
I wouldn't worry too much about stress when you bring them home, I would give yourself a day to get the cage set up just to make sure you have everything & have time to give plenty of thought to how you do it then go back maybe the next day for your hamster/s.
Virtually all hams will be a bit stressed by the change but as long as you have everything ready for them & can just put them in the cage & give them a day or two to settle quietly they should be fine.
As far as I know robos don't get wet tail btw.
The most stress occurs from over cleaning or making changes to the cage when they're new so nothing but spot cleaning pee for the first few weeks at least, if you can find any that is with a robo!