judging roof truss strength

So I tore my brick flu down on the weekend. It was in bad shape, so I have not burned wood for a couple of years. It ran up through the center of the house, and had started to leak, so I finally had to get off my keaster and get it done. While on the roof I became alarmed at how bad my shingles were, and I think I am up against a new roof. Think I will go with steel. I have future plans for a veranda on the front, and a screened in porch on the back. The house is a 24 by 44 bungalow, so was figuring on a 10 by 24 on front, and perhaps 14 by 24 on the rear. In order to save the extra work when I do the front and rear additions, I figure I will do the roof dormers now, and then I won't have to disturb the roof much when I add on. So the house was built in 74. The roof trusses are 2x4 with 2x3 spars. The area where the new dormers will be added was divided by a wall down the center of the house, but has been opened up save for an 8 foot wall from the outside wall in. Should I be ok with the standard add on trusses. The outside being pretty much the same as the existing trusses with the others getting smaller as I move in, or is there something I should do to transfer the weight to the outside wall, and keep it away from the existing roof. We do have a truss company here in town, but I am just looking for feedback based on experience.

I doubt if there is a problem with extra weight on the roof but that would be a question for the truss company, the most they would likely ask for is some T bracing on some of the webbing.
I would think what you want is a gable end for the front and back and the matching trusses that sit on the roof.
The gable would sit on the outer edge of the wall and the old trusses would have to be cut to allow that. There are joining plates in that area so the truss company would have to tell you how to deal with that.
Normally you would just sit them on the new wall or beam and then you would just cut the tails off the old trusses.
You might consider just installing posts and beams and doing the rooves complete. Build the addons later under the beams.