If you don't want to gain weight you should start the tren from the start and keep test low like you said... IMO tren ace is better for a first timer. With tren if your gaining to much weight just cut back on the food and the tren will help keep the muscle and dropping fat of you on such a low cal diet. That's the great thing about tren (even though I hate using it) eat alot and blow up with real muscle keep cal count low and the fat melts away..
Keep test at 250-300 then start the tren at 200 for 4wks to see how sides get. With ace you could ramp up much faster cuz it would hit you faster but with the long ester you need to wait 4+wks before it will reach it's max blood concentration. From there you could up it 1-200every 2wk and see how it goes but I would say up it only 100every 2wks.