Insulation from wire looks good especially if you use bits of fine wire for ties, just cut it lengthways pull the wire out cut to length and place on cage.
Wheelie bars, I use or modify kit ones.
Spoilers,depends on type. Huge pro mod types are reasonably easy, cut piece of sheet styrene to width ( usually just wider than trunk lid) sides, well the bottom needs to follow that cars body line, top just look at the same type of car (google etc) to see what shape you want/like/need. Sketchout that onto some light card ,test fit to car when happy transfer to sheet styrene and glue to the big flat piece making sure its level on both sides, when happy glue to car and blend wing deck to the body with putty.
Chutes, just find some resin ones, not expensive ,well worth it you'ld be very hard pressed to get any detail out of scratchbuilts. If you're too broke (trust me I KNOW THIS ONE) your best bet would be making a block out of layers of styrene and carving/filing to shape