What is the best way to paint the tin ware?
Get it powder coated, or with regular spray can, what do most people do?

I used POR15, brushed on, looks good

depends on what look your after. mines got 2 pac on it but then again half of its fibreglass.
powder coating looks nice though

What's wrong with the paint that's on it? I've never had to paint tinware. The paint was pretty durable from the factory and they usually spend half their life smeared with oil so I've never seen one that was rusty or didn't clean up pretty nicely with a rag.

Powder coat is best but make sure you fit the tin ware to engine first then starighten it and or repair as necessary as once is coated if u bend u will crack the coatings

The key is in the prep if you are gonna paint.

I've painted several of mine, if you spend the time prepping and use quality paint it holds up well for years.

No need for hi-temp paints, tinware doesn't get hot enough to cure hi-temp paint properly.

That said though I did have the tin on my 1776 powedercoated white and the difference was night and day to paint.
It does cost more but you only have to do it once.

Like Birch said test fit the tin first, after mine was sandblasted and powercoated there was a rust spot that showed up and bend in the fan backing plate.

Dpends what job you want. Pull it down and prep it for a nice finish. Good paint will last and a good finish looks sweet