I guess I misunderstood you when you intially mentioned portable, I thought you wanted to be able to pack it up and bring it with you like the unit I made for my friend. I traded him my original PinMAME cab which he has setup at his shop where he spent most of his time. Sometimes he gets the urge to play and sucks to have to go to your work for your pin fix and he wished he could have another one at home. So I proposed the idea of building him a portable unit he could literally bring with him where ever he goes as long as he covered costs.
If you are going to build from scratch and keep with a more traditional cab I would go for a P2K style cab and cast the DMD reflection like this on the playfield glass. Here is a video of mine on a regular piece of tempered glass and the effect is pretty good.
Just FYI, if you want to save yourself a bit of work and money you can always find an empty donor cab and a de-cased 37" LCD can drop in there perfectly without any modification. If you want to go bigger like 42"-46" LCD then you might want to find a wide body donor cab so it can fit inside or else you can always remove the side rails and trim the sides of the cab so the LCD can sit on top and install the side rails back on.
I have been debating to spend $130usd on P2K buttons only but just can't justify spending that much and it's no wonder why they are always missing on empty SWE1 cabs along with the glass, lockdown bar and signature jpop shooter rod. I have zero wood working skills as you can see my friend Drano has to cut or CNC button inserts for me through his amazing work place. Must be nice to literally eat, sleep and breath pinball at home and at work bud!
Here are the buttons you will need for PinMAME
Left Shift = Left Flipper
Right Shift = Right Flipper
Left Ctrl = Left Manga Save/Function
Right Ctrl = Right Magna Save/Function
ENTER = Ball Plunger
Z = Left Nudge
/ = Right Nudge
SPACE = Center Nudge
T = Mechanical Tilt
1 = Start Button
2 = Buy In/Extra Ball
5 = Credit Up
END = Coin Door Interlock Switch **
7 = Exit Menu (service) **
8 = Minus (service) **
9 = Plus (service) **
0 = Select (service) **
F = Pull Up Flyer in Hyperpin
I = Pull Up Instruction Card in Hyperpin
ESC = Exit Table
That is 20 inputs I marked a "**" next to the ones that are optional and since they are not used very often or once in a while just make sure you have a keyboard handy. If you are using an IPAC it supports up to 32 inputs so that leaves you with 12 inputs free. So for MAME:
Joystick = 4 inputs (one for each direction)
6 buttons = 6 inputs (assuming you go with a SFII button layout)
For other functions like Start and Credit Up you can share the same input or even physical button on your control panel. You will notice on my portable unit there are two joysticks, one is for MAME and the other is a dedicated 4-way for Baby Pacman which is one of my friend's holy grail games growing up. Both of the joysticks only use 4 inputs as I daisy chained each direction going to my IPAC.
If you are going for a 2 player MAME control panel setup you will probably want to go for the IPAC64 which can handle up to 64 inputs. Also make sure you get a keyboard encoder and not a game pad encoder. A game pad encoder does not register as physical key presses (such as the letter A or Left Shift Key) and you will need to run extra software such as X-padder or Joy2Key to map to a physical keyboard key. It makes setup in MAME more cumbersome because that means you will have to configure each game to work with your controls where as the IPAC comes with software that allows you to re-map all the inputs to match the MAME defaults.
Any other questions or if you are confused feel free to ask.