Another vote for Progressive. I've used their shocks and fork springs on all 15bikes I've build and ridden over the years. Their stuff simply works great.
Progressive has a fork spring replacement lowering kit that cost less than the HD stuff for your 'glide and offers matching rear shocks that are world's better than the factory air shocks.
It's best to make sure that your final ride hieght of the rear is compatable with the lowered front ride hieght when you go to make the mods.
Lowering just the rear of the bike will increase the rake and add to the trail and that will make the bike more stable for high speed straight line running. Leaving the rear high and just lowering the front, will reduce the rake angle and "can" make the bike more twitchy.
Also, my last .02 is that once the bike is lowered, take some time to get used to the fact that you will not be able to lean it over as far into the turns now because the floorboards will scrape sooner than they did before.
Lowering the bike, means that there is less travle for the forks/and or shocks to cycle thru thier suspension cycle, so yes the "ride quality" will not be as "plush" as the stock ride hieght because you'll have lees suspension travle available to soak up the bumps.