Prepare using scotch-brite type A "Fine" or wet&dry paper. Use a TAK rag and very light hand pressure or a clean airline to remove any FOD then solvent clean using something non-aggressive like IPA and water 70:30 mix, use the wipe-on wipe-off method, have 2 cloths, one for cleaning with the solvent and the other for wiping down before it evapourates. theres nothing wrong with using white spirits but it might be a little agressive on the plastic engine cover and you could end up with a poor primer finish. Finally prime using a specialised plastic primer and topcoat using several coats of your preferred colour. Time to re-coat is when the coating is tacky to a light touch but doesn't come away on your finger. Appearance/Gloss will be effected by the ambient temp and humidity, for most paints and primers 16°C to 22°C and 30% - 70% RH is OK.
I cant comment on heat resistance because i dont know when sort of temp the coating is likelly to see on a daily basis. But what i should mention is that the oil filler cap is located in the middle of the engine cover and i dont think anything decorative you can buy in an aerosol will have great oil resistance.