The risk in transferring the UR points now is that then you're locked into Hyatt. If there are other properties from other chains you might be tempted to book instead by a good promo from them, wait a bit. Depending upon the number of rooms and the price point there may be value in you directly contacting the hotel to see if you can negotiate a block rate or other discount, especially if you end up needing more than 5 rooms. If you are considering using the hotel facilities for some wedding-related function in addition to the rooms you should be able to earn HGP points for that spend too but you won't (to the best of my knowledge) be able to use HGP points for such facilities.
Personally I wouldn't hold my breath waiting for a promotion of any significance from Hyatt. Likely there will be something but it is unlikely to materially affect rates and you could almost certainly rework an existing reservation to qualify should a promotion of interest occur.
Your platinum benefits would only accrue to your room and not to the others.