DjSE7EN - Get the fuselage as straight as possible. You'll be glad you did and it's worth taking the time to get it right.

Here's how:

First, draw a long straight line on your building board. Put a piece of waxed paper over it. Mark the locations of all the formers on the line (take measurements from the plan). Measure and draw a centerline on each former. Line up the formers over the line you drew and make sure they are square to the line. The one exception to this might be the firewall if it has right thrust.

Use plenty of clamps, rubber bands, pins, etc to put the whole thing together WITHOUT GLUE!

Now look at it from slightly above and from the rear. If you see an obvious warp, fix it. When you are completely satisfied that it's all straight, leave the formers pinned in place and remove the fuselage sides. Put glue on all the formers and put the fuselage sides back. Pin and clamp it just like it was before. Now check it all again. If you use slow drying glue such as carpenter's glue you'll have plenty of time to get it all aligned.

As far as the firewall goes, it won't hurt to build in a little right thrust and a little down thrust.