Definitively 5 vs 5. Most of the teams are adapted to this format since it has been the default format in most of the competitions.
Most of the maps played in competition (BDX), already limit the weapons... for me it works fine.
I prefered 3 minutes.
Number of Rounds:
If 1 map, 17 rounds, if 2 maps 15 or even 13.
To build a good competition, its mandatory to have an AC software. MOSS could do the job.
All week should be allowed, but if needed to set a default day (like in leagues and tournaments), normally sundays work good for europeans and mondays for americans (right?)