If you have an iPad gen 1-4 you can use use a kit like this https://www.aliexpress.com/item/4000539812281.html to use its screen as a monitor. (that kit is only for gen 2 so find a different one for a different gen)
Depends what you want to make. Some popular designs are the G-boy (left) and the Ashida (right).
G-boys are pretty expensive nowadays though, because they've been discontinued.
You could also make something like this if you want something simple and cheap.
Those links R. G. Marigold posted...
Thanks for the info guys! If I buy this, could i wire 2 of these in series for 14.8 volts like The_Dankest suggested?
https://www.ebay.ca/itm/384599395736
Okay I think I have my plans mostly worked out. if I use an untrimmed motherboard is there any cheaper way to power my portable than doing this?
https://bitbuilt.net/forums/index.php?threads/custom-regulators-an-explanation-and-guide.754/
I want to make a simple portable Wii, basically just a stripped down Wii with a screen and a battery, to minimize the cost. I am a total newbie when it comes to this stuff though, so how would I go about making that?