Could a diy fightstick like this work with PoE2? How many buttons wpuld I need?

For anything other than fighting games, I'd go with the WASD movement layout instead of HitBox style.

POE 2 has official controller support, so you just need to replicate it accordingly. 2 analog sticks, a 4-button d-pad, about 10 action buttons, pause, select. 

Bare minimum:

1. joystick for movement (this can also work for aiming, you don't need a second)
2. 1 button for main skill and to interact (can be same button but is annoying)
3. 1 button for exit/cancel, this can also be assigned to roll/dodge or health flask.
4. Menu button.

You can now play and probably even beat Arbiter!
Note* mana and health are gonna be difficult since no buttons are assigned to flasks yet. So go for a health/mana regen build.

Additional useful buttons:

1. Start button, this will allow trading and pausing the game (note, you can adjust all settings before you login without a start button (display, button binds, item filters, etc)
2. Button for health potion will be quite helpful, otherwise second attack.
3. Button for the map display is really nice!
4. Everything else is 'more buttons for more attacks', but there are plenty of 'one-button builds', so this is purely preference.

An unexpected overlap of interests! I've used leverless controllers a bunch and it's doable but certainly wouldn't be the first pick for me.

The standard asd+space style leverless layout is specifically designed for fighting games and can be annoying in some games that actively use up/down (Celeste comes to mind, shmups, anything isometric, etc.). If you're going for a generic 2d retrogame controller, I'd suggest something like the wasd style mixbox layout or at least an extra button above 's' for a hybrid. You could maybe play a melee-only build without using the right analog stick if you get the targetting settings right but that's extremely limiting so you probably want sticks. No idea if there are any pre-made PCBs available with analog sticks in mind so that might be something you'd have to handle yourself. 

All in all it's going to be a lot more effort than a regular leverless. If you're willing to dive into a diy project, something like the Junkfood Arcades SWORL might work as an inspiration. I'd just use a regular pad though lol

WASD + 7 buttons + shift (for alternate 7 buttons) + spacebar (dodge) + escape (for menu). ~~So 13~~. I forgot, subtract out 3 buttons on mouse. 10.

You don't need to print up something, You can just buy a left hand game keypad.

I don’t understand this question. You can play poe2 with a controller comfortably, and this doesn’t have any less buttons. Are you concerned about losing the back triggers?

Do some key binding and should be just fine

As someone who's used to using interesting input devices, including several variations of leverless controllers, I'd recommend something like this:

https://i0.wp.com/arkodd.com/wp-content/uploads/2025/11/20251012_092416-scaled.jpg

I just picked one of these up not all that long ago and it works pretty well for lots of games. It's nice that there's a left shoulder button in the design too, so you don't have to miss out on that functionality or use a face button to shift between hotbars. Probably not easy to create from the ground up, but I've been enjoying it with PoE2!

You only need one button to cast spark soooo...

you still need keyboard anyway. to list item, regex, etc.