The XCR resin is very good but, as it is quite thick, it will retain a lot of air after mixing. Gently warming it will speed-up the de-gassing and make it go on quite well, but be careful as it does cure quite quickly. It's also a good idea to cover your just-brushed parts to limit the amount of dust particles that will invariably fall onto it, leaving small nibs and eventual holes when sanding. 

You can get a small scraper tool that holds a razor blade in places like Wilko (if you're in the UK?) and this is really good for shaving-off small lumps of resin and drips which will save a bit of sanding time with the coarser grits.

Despite the resin being quite good on vertical sides, I've always found it best to coat parts in stages so that surfaces can cure horizontally, so leaving a 'flatter' starting point. You can also think about using 240 grit as a start point if your cured part is not too bumpy to begin with but, with even the most careful blok sanding, you'll usually find your self needing to re-coat at some point if visual perfection is required. Of course, the amount of sanding might be reduced if you're only going to a stage required as a key for final spray clear-coating with an automotive-grade product, but getting an excellent finish on anything but smallish bits will always be quite a labour-intensive process if progressing all the way to 1500 or 200 grit for a gloss finish.