Can't use the DS-lite screens I'm afraid, you have to use a screen and driver board that takes standard video inputs like composite and VGA.
For softmodding the Wii, youtube has many videos on how to execute LetterBomb and install the Homebrew Channel and Priiloader. After doing that,
read this post and follow the instructions to install RVLoader, which will be the software that runs your games from a USB drive.
Emulators are pretty easy to install, just search for the console you want on
wiibrew.org and read the pages for the emulators and try them out. Just remember that if you trim the Wii you will need to relocate the MX chip for some of them to function.
If you want to rip any disks you
own,
you can use a Wii homebrew app called CleanRip. It will rip the disk image to your USB drive, so make sure you're using a drive large enough to hold all the images you want, or you'll have to do them in batches and move the files to your computer for storage. I'm unsure if CleanRip creates .iso or .wbfs images from Wii disks, so if it ends up making .iso files you will need to convert them into .wbfs files yourself on a PC. You will also have to manually adjust the filenames and move the files into the correct folders for RVLoader to be able to see them. Btw we legally can't help you find ROMs online, so please don't ask.
All the currently open source case designs use trimmed Wiis. Mostly the standard OMGWTF trim. Gman sells his beginner friendly G-Wii case, PM him on the forum if you want to buy one. Else, you'll have to design/build a case yourself.
3DS sliders can be good for very low profile designs, but we mostly use Nintendo Switch joycon sticks now. Some larger cases like the G-Wii just use the original Gamecube controller sticks and buttons, which is generally easier for a first timer and we generally recommend trying a G-Wii first.
As for advice, I always recommend having a scroll through a couple of dozen completed systems in The Cutting Edge and having a look at the internal shots to get an idea in your head of the basic design and assembly principles, then checking the worklogs for those builds in the Wii section to see the "step by step" on how they were assembled, what challenges were encountered, and how they were resolved. This isn't a hobby where anyone's going to hold your hand, but if you spend the time and do the research, ask half decent questions and listen to feedback, I'm sure you'll be able to do it.
Also building a portable can be hecking expensive, so be prepared to spend at least $600 in parts, replacement parts, and tools.
Check the above paragraph. For the touchscreen, it is possible, but you'd have to either contact JacksonS (the last guy to successfully achieve that) and ask about his implementation, or design/program/assemble your own bluetooth module emulator. You don't really need touchscreen though, as RVLoader features a Wiimote emulation software that uses standard physical Gamecube controls.
