Hi RcBruder!
I think you will be fine with running all three motors on the same speed controller. I run four on the same controller in my version.
For inspiration you could have a look at my low-cost build here:
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http://www.scale4x4rc.org/forums/showthread.php?t=80393
It's not the same Bruder truck, but I believe the rear end is exactly the same. The front end is a bit different. I wish I had used your Bruder model for the build. It looks much better, IMHO.
All the 3D-printed parts are downloadable for free, just click the links in one of the later posts.
Best regards,
Stein :-)