I want to make my first custom paintjob for the SDCC Transformers Prime Deluxe Optimus Prime, but I have no idea where to begin or what I need. Please help.
There's a subforum dedicated to questions like these: Creative - TFW2005 - The 2005 Boards Look around there are plenty of tutorials and people willing to help. It would also help if you gave us some idea about what you want to do.
Do you even know what it is you plan to make of it? And I'd suggest waiting on the regular Deluxe release, rather than using the SDCC Exclusive for a custom. (I say that, but I've customized the SDCC Nemesis Prime.) You'll find everything you need in the Tutorials section of the Radicons sub-site.
We have nearly 500 tutorials here, which is the most dedicated to Transformers found anywhere. encline has contributed to them as well (along with many others over the years)