Probablly get different responses to this, but heres what I would do :

Drop it 25mm
I would go for a single 4" exit exhaust (not into twin exits myself)
Any escort shell will be ok for converting, although some strengthening may be required in certain areas
With regards to spraying, bit difficult question. I reckon to spray the bits you mention it will cost about £200-£300. As to wether you should respray the whole car or not, ask yourself a) is the car paintwork any good as it is? if not then a whole respray would be a good idea, b) will the sprayer be able to do a good match of the bodykit to the color of the car? if not, then a complete respray would be best. Also, if you wanted it to be a good replica then you are probablly gonna wanna do a full respray because I dont think the bonus come in a colour that the rst does ? (maybe red?? im not sure)
With regards where best to look, keep an eye on your local paper, RS forums (like the for sale section on here) and of course ebay! there is another thread on here from a couple days ago that I responded to about what would be need in the engine department etc...

CheeRS