Hi Eric B 125... welcome back to windsurfing!
Your UltraCat is a great longboard (they are still raced very successfully) but to get shortboard planing performance, the UltraCat will never give you the same feel.
Since you have the balance mastered (on your UltraCat) the transition to short board
should be fairly easy.
What sort of wind speed do you have on your local lakes?
A 7.0 m2 rig on a Futura 144 sounds a bit small.
Your UltraCat goes "through" the water quite easily, but with the Futura you will need to
get up on top of the water and that basically requires a larger sail.
If you are still using the sails/mast/boom that came with your UltraCat (or is of that vintage) you are in for a treat with the modern sails/masts/booms.
Modern rigs are much lighter!
I would suggest an 8.5 m2 rig for the Futura 144. Get a high carbon (or 100% carbon) mast that weighs about 50% less than your Vintage Fanatic UltraCat rig.
Add a carbon boom to keep the rig weight down and you should have a really great
board/rig setup for winds up to around 15 knots.
Try to make sure the mast is compatible (buy the mast and sail from the same manufacturer)) with your new sail (s).
Hope this helps,