so, you have a shed at least, that's great. i personally would leave the smoothrite in the tin... especially seeing as you're going to give it a good rub down anyway...
use the 240 grit and plenty of water to rub down the edges. the rough cast centre and spokes respond to and only need a scourer to key their surfaces. mix up some filler and apply sparingly to any dents / imperfections. when dry sand again and when happy that all is smooth mask the tyre, valve and weights. (start with 1-2 inch tape lengths tucked in between the rim and tyre then double thickness newspaper around the rest of the tyre) prime any areas that have been worked on only. when dry sand with the 400 grit and some water. panel wipe the whole wheel and then colour it all over. 2 coats is enough. when dry 2 coats of lacquer is enough, i usually apply 3 for added protection and shine depth. i usually put my finished wheel in front of the lounge fire for an hour, this doesn't go down well the long haird general but does bake the paint nicely.
concept chemicals primer £4
concept chemicals gloss black (or silver or gold) £4
concept chemicals acrylic lacquer £4
1/2 inch masking tape 86p
p40 filler around £5
240 and 400 grit wet 'n' dry papers £1.50
panel wipe £4
i appreciate that above list will be near to £30 but it's all that you'll need to achieve a professional quality finish. the quality of the concept chemicals paint is fantastic and it's easy to apply too. i painted my van wheels with the stuff 7 years ago and there's not a single area of any of them that has failed or deteriorated in any way. well worth hunting down in your local paint factor, don't assume that halfords paint will do, it won't!
here's how my rear wheel turned out:
and you have the benefit of being able to touch in any future imperfections caused by tyre and balancing weight changes.
hth