What I say probably echoes pervious comments (which I didn't read all of).
If your models are losing details and your brushes getting ruined its likely that you're using too much paint and not using any water - which should protect your brushes (they likely have paint drying on them, etc). Using a palette (even your hand, that's what I do) should alleviate much of this - as you can thin the paint out (with or without water) before you apply it to the minis. Half a pot on WoMT shouldn't ever happen - I've used Chainmail on all of my figures, this got me through the armor of 2 boxes of orcs, 3 boxes of warg riders, one box of Uruk Scouts, one box of Morannons, one box of Galadhrim, a Mordor Troll and a Winged Nazgul (which, yes, didn't have many metal areas) but I think the example stands - and I still have about 25% of the pot left. I think you've been using far too much paint - fix this and use a palette, even if it's your hand and you should be fine. The rest falls into getting used to painting minis in the first place - and you'll only get better and better as you go along
Hope I helped.