I am currently finishing off the first 'pumpkin' ale I have ever attempted. I used 3.5# butternut squash in a 6.5 g batch (that I grew last year- I still have some- I can't believe it kept) that I cut into 2" cubes and roasted at 350 for an hour and a half (cooked down to 3#) It is quite delicious, unspiced and I used a brown/ robust porter malt bill. The pumpkin flavor is very prominent from start to finish and is quite aromatic. You could use half the amount that I did and still get significant pumpkin flavor.
I just stirred the cubes in on top of the mash and used .5# rice hulls- I doubt it was really necessary.
I am biased toward dark ale but I do feel that the amount of sweetness that the pumpkin/ squash lends to the beer can be balanced by darker malts or mashing low, dry because the body will still be there- too much lighter crystal malt (< 60L) will likely be cloying.
It's worth noting that most canned pumpkin is actually hubbard squash. IMHO the winter squash all taste similar with varying degrees of sweetness/ fruitiness and orange pumpkins are bland compared hubbards and buttercup (my fav.) I think it would be interesting to try 1# butternut and 1# acorn (closer to pumpkin) to mix the flavor characteristics just like we do with all of our other ingredients.
Also worth noting: squash is high in magnesium so you can forego yeast nutrient unless you want a metallic twang. I think.