Hi.
Yes, I see a problem : too much metal washers can damage the thread. I did it for a long while, till I was told it could damage. I suggest you to use nylon washers except for the first and last ones. I mean, you can put as much nylon washers as you may want/need, but you'll have to insert them between the two metal washers. That's what I do.
Another tip is using a kind of tube you can put between the upper and lower washers, for instance socalled 'spacer bushings' (or 'bushing spacers', I don't remember).
The best is here :
http://www.manitopercussion.com/lug-extenders/ Depends on where you are located. In my case, the shipping costs were higher than the price of the product itself, so I didn't order them and made my own, buying and cutting a piece of tube in a DIY shop.
And here's another tip : a famous conga maker, who is well known on this forum, taught me once that "steel eats steel". That's why he uses bronze nuts on his lugs, to preserve their thread. I follow now his advice, and use now bronze nuts too. If youre lugs are in metric system (I live in Europe), use brass or bronze exhaust manifolds nuts from Fiat 500 (in M8, 8 mm diameter).
If they're in the imperial system, either 3/8" or 5/16", use then Mini Austin brass or bronze manifold nuts. You also should be able to find some in ship supply shops or sites.
If you use nylon washers or tubes, and bronze nuts, you can't go wrong.
You can also have a look here :
http://www.manitopercussion.com/products-page/custom-hardware/set-of-6-tuning-lugs/, especially on the 2nd picture
http://www.manitopercussion.com/wp-content/uploads/2013/09/1-DSC_00091.jpg.
Hope it helps.