BMX/MTB Crank compatability

[Supa C]

I have noticed that new school bmx bikes often used MTB cranks such as saints. While shopping around I have noticed there are many alternatives with the 2 piece, outboard bearing design. I have been getting information overload with all the different specs.
If one were to choose a diferent model than shimano saints, or DXR, etc.. what numbers are important to look at so that you still get a good functioning drivetrain?

68/73 with spacers?
105mm 4 bolt spider?
Will any of the 2 chainring designs work?

What are some numbers to absolutely avoid?

Thanks in advance for any educating that goes on here.

Chris

[Supa C]

here's what I learned:

Road cranks will line up with no mods.

MTB cranks will be a little wider than standard bmx chainline. How much depends on the rear hub, adjustability of cog on the cassette, and spacer setup on the BB.

Most of the cranks that are more affordable are not available in 180mm.