I bought a cheap (£45) Oxford pair of heated grips, and they are very good, no problems so far .. just fit to handlebars and connect 2 wires [+/-] to the battery. Its a better earth connection this way too, rather than connecting to the bike frame, I found.
good luck with the DR .. good bike, great engine, but keep on top of maintenance (carb, brakes, suspension, bearings, etc and fit good knobblies (MT21/ Mitas E09/ IT/ XT644 whatever) as 50/50 tyres are not so good for more difficult trails (my own opinion).
when you are happy with the bike, do a few easy tracks, like you been doing, then join a club, like the local trf or local bods.
.. don't ride beyond your ability, if you fall behind they will either come back or you will be picked up by the `sweeper` .. or both in my case
happy riding
ps ... make sure the throttle openings (twist grip) work properly, and that idle is ok at the correct revs,
and make sure the brakes work perfectly .. not binding and not snatchy on/off (personal DR experience
> 2 years limping)