Hiya and welcome mate!
I shall attempt to provide info that will keep the costs down without sacrificying quality.
Engine: Personally I would stay with a .28 (fuel consumption vs performance gain is nominal but your choice) "GO! Engines" have a high reputation, engineered in Germany and perform well (I don't own one,,,.yet) Link to ebay shop HERE Link to website HERE If you want a dirt cheap ofna force engine pipe unit, PM me.
Wheels (maybe a 17mm conversion?): Unless you ran a Lightning stadium sport which has 14mm hexes standard 17mm truggy wheels will fit. If you are thinking of the 17mmaxle conversion see my sig I run Proline Wheels always usually with Badlands tires 3.2 (not shown in sig) Others run from the ansmann range which are cheaper.
Shocks Stock shocks are good If u need new ones Ebay is agood spot for cheap ones. The plastic eyelet on the shock cap can break and Hotbodies have some complete alu ones (though colour choice is limited; purple) MyDoody has good links for alterntives, bear in mind it is difficult to find the exact size; (lengthwise)
Shock oil help: A lot run 40k + or 45k. I run 40k on my local BMX track with good results I am needing below 1/2 of that on the race track, My next track setup will be 15k front 10k rear.
Diff oil help Diff Oil here has been a confusing issue here. note "Wt" and "Cst" are not the same Cst is considered to be the most accurate method of measuring the oil thickness
Shell + Spoiler: Ebay Uk has em both at the mo. You may wish to contact CreativeChris if you want something different, he has various other bodies slightly modded from the Savage range.
Servos:
[*]Do I say it lol,.Sav