Ok, so i'm going out on a limb here and making a replica of my boyfriends truck for him for his birthday in april.

It's a black truck tips on making the black fondant shiny?

What about the support system, his trucks kinda long and i feel like it will sag in the middle because thats where the most cake will be? it's a lifted truck so I want it to look as real as possible and was going to try and make it so it didn't have anything underneath it that you could see.

Also and idea for what to put the cake on. I don't think the cake from the truck will be enough and I just want a little extra. I was thinking a rectangle cake and make it look like a road and place the truck on top.

AHHH I don't know. Please let me know what you think!

Any other tips for a first timers cake?

It depends on the type of fondant being used. Store bought may take a shine a bit better than marshmallow. I use Marshmallow exclusively because I feel it is better if the cake is enjoyable to eat as well as look at. The store bought stuff taste terrible in my opinion. I think that there is some kind spray that shines it up nicely. Remember that the more shine you get the more it will show the imperfections in the fondant surface. Black cars show every little door ding and scratch in real life, a dull surface will still be effective in representing the truck and not show as many surface imperfections.
Making a truck cake is not really beginner territory but depending on your mechanical ability it will be a good challenge for you. If this is going to be a 4x4 then the whole cake should be lifted to show the suspension details. I make all of my own custom supports out of clear acrylic, but this is getting kind-of technical for a novice to try. You could try a simplier version by going to Home Depot where they usually have cut off remnants of Plexiglas that they might cut to size for you, then get four pieces of 1/2 PVC from the irrigation dept. Cut them so that they can press through the cake and still have enough length to give a lifted truck look. then set the four pipes in the wheel locations. Then place the plex on top of the four pipes and now you have a raised platform for the truck body. This is not taking into account any type of fastening method from plex to pipe. Screws work well but plex must be predrilled to avoid cracking.
Wheels could be Hostess Ding Dongs or Big Wheels. Use the PVC pipe to cut out the middle to give a center wheel look.
Sounds like a fun project have fun.