i want to start a gestalt in RotRL with 25 point buy, will only 3 players be an issue considering the power level? Also can you give me any advice for RotRL or Gestalt?
Gestalt is really not THAT much more powerful than standard characters unless its in the hand of true optimizers. Generally they just allow more options and help cover what would normally be weaknesses in the party. They don't gain access to higher level spells any faster and they still have the same number of actions each round as three normal characters would.
If you're concerned, I'd recommend upping the hit points of the 'bosses' (max would probably be fine) and then always keep an extra wave of mooks (3-5 goblins, 2-3 ghouls, 1-2 giants, etc.) in your back pocket. If a combat seems to be going too easily, send them in on round 3 or 4 to spice things up.
Also remember that not every encounter needs to be a serious challenge. Its fine for PC's to roll through an encounter now and then - just try to make sure the fights that should be challenging are.
Other than that you'll have to ask more specific questions if you're hoping for specific advice.