I generally play with 2 others. One guy is really good about spotting but he usually tees after me, and I walk out to spot for him. The other guy is an ADHD nightmare. He tees then sprints down the fairway standing in your line, and he never spots your throws. Actually he needs to learn basic etiquette, but that's another story. I've nearly hit him on tunnel drives at 175'-225' because he was between me and the tee. At this point I just throw. If he gets hit so be it, but I digress.
4 does seem a tad bulky, 6 would be good based on size and weight if it were circular.
You're correct for pdga that wouldn't be allowed, but I'm nowhere near there yet.
Also for RFID, it depends on the type you are using. http://www.rfidlabeling.com/tag_types.html
The kind we all think of (square antenna style sticker in dvd cases) are passive tags. The range on those can't really exceed 2 meters without being huge.