Modeling Question

I have downloaded a Truggy Trailer from Thingiverse. I am working to convert this trailer for a buddy of mine for his use. I get ready to print it and it is not doing too bad. I have 4 double bead lock rims completed. I have 3 parts printed for the rear deck. I need to print the front parts of the deck and some misc parts and suspension parts and I will be mostly there. After that I need to be able to go in and do some serious editing. Problem is I do not know what I am doing. I work in AutoCAD.... I need to take these models and be able to cut parts of them so I can I can print them as the frame and all of the middle parts are too big for my print bed. Once I can cut them up I can print them, Take them to him and find out what we need to edit from there. I know I am going to make a custom ramp that will fold up and down, and Have that already designed in my head so I will need to model it too. Can anyone recommend a good tutorial or something someplace to teach me how to cut parts and all in 123D. If not can anyone recommend something I can download and use that is free?

As soon as I get this completed (It is a paying job) I will be ready to go in and do my Auto Bed Leveling, and the new zstop mods. After that I want to put some lights on this thing so I can see it print.

Right after that I will be doing the homes I bought this for.

Pictures will be posted of the trailer later when I get them cleaned up and enough printed so I can show what it is.

Also I want to take them out to the garage and try a part or two out in my bead blast cabinet. I think if I hit them with a little walnut shells it will really dress up the finish and then I can hit them with some flat black. After that some custom lettering and this trailer will be ready to show off.