I will try and have a dabble at it.
I think this shouldn't be to hard, but could you make scenery from the game vehicles? There are crashed walkers and transports from BF2142 and this would look strange if they where not updated.
Also could you make the titans look like the ships in the space battles from Battlefront 2? It's a great game.
And now to answer your questions.
There will be no BF2142 scenery in First Strike. All scenery are created anew and are Star Wars related. So if you see a crashed walker, it will be a AT-ST or AT-AT.
The titans are not going to be in the game. There are capital ships like in Battlefront, but they are far more accurate then the ones in Battlefront 2.
And inregards to your last statement. You will probably realise that Battlefront 2 is a heap of Bantha pudu, when you start playing First Strike.