First Rocket

I guess you could do some simple maths, based on newton's laws and change in momentum, but you need to factor in drag.
Far easier, grab (for free) WRASP - a simple rocket simulation program. Alternatively RockSim is a very powerful design and simulation program, and SpaceCAD is easy to use for model rockets. Both have free demos available.
Estes rockets are pretty much a known quantity, for a given BT size and motor, and 'standard' construction you'll usually get about the same altitude. If the Stormcaster is Bt-60 (about 40mm diameter), then on a D12 you'll probably get 6-700 feet, perhaps more (I think anyway, my heavy BT-60 rocket with altimeter did about 5-600 feet on a D12).
Welcome to the hobby, prepare to say goodbye to all your time and money ;-)
Happy flying!
-- Niall Oswald ========= UKRA 1345 L0 EARS 1151 MARS "Gravity assisted pieces of the rocket raining from the sky should be avoided. It is also financially undesirable." -Portland State Aerospace Society

Here, launch it all you want for free: Joel. phx

Welcome! Enjoy the hobby. Keep flying.
Nick

My nephew flew his first rocket last week which was the storm caster on a D12-5, it was cool, but it was lost in the bush.