I totally agree with ChristopherB. Also, speaking from experience, a very effective paint remover is called Scalecoat. This media is spefically designed to remove paint from any plastic of resin parts without consequences. The paint that needs removal does not require soaking of parts. It is very easy to use and can be done by just swabbing Scalecoat over the paint to be removed and after a few minutes just wipe the paint away.
A VF-1J Reisssue is the most recommendable walk to use as it required only removal of the red paint that destiguishes to be a 1J. The other marking can be left alone and will give you a much cleaner and more orginal look to your custom.
With regards to the resin items, all parts must be cleaned, sanded, filled, sanded, primed (this is my method of choice), as it helps to remove imperfections from the recasted items. You can use a paint from Krylon (Smoothest Finish) grey to completely match the original color of the VF-1J plastic.
I have posted several pictures of a VF-1A low vis that has this technique applied to it. Mind youm this was the first time I used Scalecoat and Krylon Smoothest Finish Paint, with exemplary results. Search for the thread the pictures are rather large but you'll get the picture.
NOTE: You will note that the metal parts are the only painted items, while the blue parts are actually dyed (Plastikote, Shale Blue).
Good Luck on your custom, and have a blast doing it. Don't forget to post pics of your progress.
Late',
NB4M