Tyres/ Tubes: Rotational weight makes a huge difference to how you bike handles. Whilst the hubs are far from lightweight, the stock rims are light enough to avoid having te replace the wheelset. Holy Rollers are overkill for the kind of bike you're looking for. Instead, I'd go for one of the following:
Kenda Combo: A Kenda NPJ Sig rear tyre, matched with a Small Block 8 front. The NPJ is nice and light, with minimal rolling resistance. The SB8 is quite a grippy 4X/ DJ tyre with a minimal weight penalty. From memory the weights are ~620g and ~680 respectively, as compared to a Holy Roller I think is almost a kilo.
Schwalbe Table Top: The TT is a very lightweight tyre with slightly less tread than a SB8 but a little more than an NPJ. The sidewalls are quite thin and the tyre profile is smaller than a Holy Roller, but it offers reasonable grip at ~580g.
There's a few other options around but these are the more popular ones. Whichever ones you go for, make sure you run lightweight tubes. DH tubes are overkill on the type of bike you want, and will make the bike feel heavy and sluggish, particularly in the air. Maxxis Welterweights are ~170g, and when inflated to the correct pressure should be resistant to pinch flats.