tagging several houses on a street with streetname and postcode

In Potlatch 2, unlike Potlatch 1, (and JOSM) you can select multiple objects by holding down control while you click them. In this way you could draw all the objects first, then select all those that you want to add the same tags to and add them to all of those in one go.

I do not use Potlatch, so better answers might come, but the easiest way to me seems this:

1. Create all the address points
2. Create one complete address (even with numbers so that you do not have to add addr:streetnumber more times)
3. Click on each addresspoint and hit R
4. Go through the address points again putting in the correct numbers

Remarks:
R copies the tags from the last object that was selected
You have to unselect a newly created node for R to work (a bug maybe?)

Or (expecially if the street has consecutive numbers) consider using JOSM - it has address interpolation. If you do this, please place the numbers precisely beacause searching for the number on the map to correct this is really annoying.