Hope you enjoy, glad it'll get some use...

Fusion360 is a no brainer - even if it wasn't free for us, it would still be one of the best options in my honest opinion. Very, very capable bit of software these days.

As Boyan says, given that you are starting from nothing I would personally suggest mach4. It's started to mature a bit in the last few months and I've been very happy with it recently... mach3 has the benefit of years of use behind it, but it's a dead end now as far as development is concerned and it is old tech compared to mach4.

That does limit you to certain motion controllers, but again I would suggest buying something decent here with the money you saved on the machine. When time comes that you decide to move on to a bigger badder machine you can take the controller with you... Cheapest good option for mach4 is probably a pokeys57CNC (although from what I've read boyan struggled with it, mine has been flawless thus far... I believe he was mostly struggling with mach3 and the pokeys board). They do make separate driver boards too which you would probably need for the steppers. Do break open that box though and see if there are some stepper drivers in there already as I doubt they were running off the main control board directly.

More premium but still affordable end you would be looking at a csmio/IP-M which recently released a mach4 plugin... again you may need some drivers to go with it.

Good luck!