Ok i really have no clue what i am doing but been repairing bathroom over the past year. I do live in a 92 doublewide so quality is about a 2 out of 10. Anyway the floor was rotten so i tore everything out around the tub. Floor and walls replaces. I replaced the drywall with the purple stuff and then desided to tile around the tub. I was planning on just putting the cement board over the drywall and tile? I been reading this is not a good idea but will it be ok? Do i paint the drywall?

Cement board and and an actual moisture barrier.

While tile is often waterproof and impermeable grout is NOT impermeable.
Water wicks through it just fine.

All the extra layer does is make the wall stack up 'different' and harder to deal with.

You will end up paying more in little details over the cost of the project.

Do not do that.  That will be lower than 2/10 quality-wise.

Take off the drywall.  Install cement board.  Paint on some RedGard (or other moisture barrier) over the cement board.  Use thin set mortar to lay tiles, then grout and seal.

As mentioned above, screw the hardi board to the studs, tape the seams, and then apply redgard to the hardi board.  The redgard is the membrane that will keep moisture out of the wall space.  Do not leave the drywall on the wall.

You can also buy Schluter kerdi use unmodified thinset to install it and the tile it. Tip I always never set the substrate on the tub I leave a gap that water cannot contact the substrate if water sits on tub ledge area. Bostick makes a thinset just for schluter systems. Keribond from mapei works good also.