What's the best activity type for Lasertag?

There is no wrong answer. What you did will work fine. For indoor, copying the Cardio APP can be done too so the GPS does not need to be disabled.

I tried to use a training to have an activity / pause structure. But it's to confusing as I don't really see if I hit pause or forgot it. I'm used to that in strength training the screen gets inverted in the pause state, but that dos not work for walking.

Do I have to create a duplicate of the strength activity (would not really like that as it will try to detect what I am doing during the active phase and I later have to clean that up) or are there other possibilities to clearly visualize that I am in a pause?

I still don't have a solution, I tried HIIT to get that inverted screen during pause, but when I convert that to other I lose the lap information. 

I went back to using a "other" activity with a plan of 40 x "running / pause".

Advantage: it is already "other" and therefor the laps don't get lost when converting.

Not that good: I don't get the inverted screen during pause, but I was able to create a data field that shows me "play" or "pause" with appbuilder 5.

Also not that good: that activity types summary really seems to be made for outdoors activities, pace is prominent on the front page and of course is 0, Speed is not existent, time in movement is 0 even though "active time" can be viewed on the laps page. First round is listed as "pause" for some reason on the "all" screen, but shows correct on the "active" and "pause" tabs. Of course no data in distance or speed, something like average heartrate would be useful.

I disabled GPS and therefore made it an indoor activity, that should remove all GPS based data evaluations.