Yes, you can replicate it using the in-game livery editor. However, due to the major differences in the build of the car, the street Evo that use to replicate the paint on will not perform exactly the same as the HKS Evo. You may also run into small problems with the replica paint due to the differently styled/shaped bodies of a street Evo vs the HKS Evo.
Personally, once the logos are done (a few hours) the design itself would probably rank about a 3 in terms of difficulty. It’s mostly just laying out some basic stripes, nothing particularly complex. If you’ve got a good level of experience with the livery editor, I’d estimate no more than 10 hours from start to finish. If you’ve never used it before it’ll take quite a bit longer if you’re going for max quality, but I still can’t see it taking too long.
The paint will NOT be transferable to any Forza games on the Xbox One. You can, however, transfer the design in the form of vinyl groups from FM4 to FH1, and FH1 to FH2 (only the 360 version of FH2, not the X1 version).
I never searched the storefront for an HKS Evo livery. I’d assume it’s been done before, but to what level of quality I don’t know. If you haven’t searched for it yourself just yet, simply go to the Community tab > Storefront > Search designs > Set the manufacturer to Mitsubishi and enter the custom keyword “HKS.” The results will show all designs with the filename or word “HKS” in the description. From there you can select your favorite one and either download it locked (don’t forget to rate it) or message the creator asking for it unlocked. Be sure to make it clear that you only want it unlocked so that you may study it, and that you have no intentions of selling or redistributing it. Most designers will not do unlocks thanks to people taking advantage of them, but there’s a chance that a generous person will be happy to give you the chance to study their paint. In the event that the creator agrees to unlock it for you but asks for a large amount of CR in return, it’s possible that the design is in fact stolen and the person trying to sell it to you is not the original creator. Some designers honestly just need the money and there is no foul play involved, but keep it in mind so that you don’t end up paying a thief for someone else’s work.
If you choose to start it yourself from the ground up, start by getting as many reference pictures as possible. This is key in making the design accurate, as well as knowing what goes where. Once you’ve got your reference pictures together, start making the logos that the design will use. Use the Create Vinyl Group feature so that you can make the logo very large. The larger the logo is while you’re making it the easier it is to spot imperfections. Once you’re finished with the logo, group all of the layers together and size the whole thing down to something like 0.05. Once you’ve made it considerably smaller it’s best to try to reset the group’s sizing to 1.00 so that you can adjust its size more specifically later on. The way I get the group’s sizing to reset to 1.00 is to ungroup all of the layers again, select one layer and randomly move and resize it, press B to cancel the changes to the layer, regroup all of the layers, and the size should now be 1.00. This will allow you to make the logo larger and smaller in much more specific increments. Play around with it and I think you’ll see what I mean. When the logo’s size is something like 0.05 it’ll get larger and smaller in very large increments. When it’s at 1.00 it’ll get larger and smaller in much smaller increments. Once that’s all finished be sure to save the file and start on the next logo. Once you’ve got all of the logos done move on to putting them on the car itself. Depending on how you like to work, you may prefer to put the logos down first and then use them as reference for the stripes’ positions, or you may prefer to put the stripes down first and then use them as a reference for the logos’ positions. There’s no wrong way to do it, so do it in whatever order you please.
I apologize for making everything so wordy, but I want to be sure that I cover most of the bases in one post instead of leaving you with a bunch of gaps and questions. Anything else you want to know, just post on here and myself or someone else will answer you. Good luck!