I just sold my HF but iirc it had a front lip that was about 1/2" deeper (taller) than the rest of the crx's. The passenger side mirror was absent (had a factory blockoff plate). No rear wiper. It did have a raised plastic spoiler on the back. Only half a radiator and gears 3,4,5 were overdrives. You could go 55 in 2nd gear if you really wanted to
As for yours. Looks nice! After sifting through a length thread on undertrays I gleaned that it's really going to depend on your particular vehicle if an undertray or lowering is going to work. In general terms undertrays(full belly pans) tend to work better on taller vehicles than on lowered ones...at least that's what the thread seemed to infer. It appears yours is already lowered.
Instead, you can easily do side skirts, make a bigger front air dam/lip, block the grill substantially (like you said you were gonna do), fill in the slits between the body panels (hood to headlight to grill etc), do a factory blockoff plate on the pass. mirror (if legal in the UK), LRR tires with mooncaps if you like, wheel skirts, wheel dams/spats too. You may be able to swap in a 5th gear out of an HF. I recall guys doing that on 1st gen crx SIs...don't know about 2nd gen though.