Once you did the oil wash, did you finish up with either a glosscote or dullcote?
I have never had trouble with this technique using Tamiya acrylics with an oil wash and then finishing up with a dullcote or glosscote to seal everything up.
My steps:
1. Base coat using Tamiya acrylics
2. Glosscote using Future
3. Decals
4. Light glosscote of Future
5. Oil Wash (Thinned w/ OSM)
6. Dullcote (Either Model Master or Poly-S acrylics)
Don't worry, based on RT's previous MPC releases, you should be able to pick these up for $40 6 months after they come out. That is unless you buy them from the RT.com store where they sell all their merchandise at prices that are above MSRP.
I would lay down your base (your models most dominate color) coat using a rattle can of spray paint.
Its just too hard to get a smooth finish on a model using a brush and if you don;t have the means to get an airbrush the next best thing would be spray paint. The brushes would be great for details and smaller parts as was stated earlier.