Help design my IPA grain bill!

Panning on ordering grain tomorrow for an IPA style beer although I'm not looking to stick strictly to the style. Basically I'm aiming for full body, high final gravity, high alc and high bitterness and heaps of hops. I want a malty biscuity flavor without being too sweet. I'm looking for suggestions on malt selection / quantities.

I like the idea of using amber malt for the biscuit flavor and Maris otter for a nutty character but have no idea what sort quantities to use or even if this is a good idea as I have never used these grains before. As a rough start I was thinking something like:

80% pale malt
15% amber
5% Maris otter

Mash at a fairly high temp and aim for around 1.070 SG?

I'd love to hear people's suggestions on what sort of grain bill would work best for what I am aiming for.

Cheers!

5% maris otter isn't going to have any really meaningful flavor contribution. It's just a slightly more flavorful base malt (and it does tend to contribute a bit more sweetness as a base malt versus pale/2row).
I like that you're working around something simple, though. I would bring up the amount of maris otter drastically (bring it up 50% or replace the pale malt with it entirely) if you're shooting for a nice malty body.

As for mash temp, hops can have a definite sweetness as well as alcohol, and with a high gravity of somewhere around 1.070 OG I would mash low and try and get very high attenuation and more alcohol. With a mash temp like 155 or similar you would more than likely end up with far, far too much body from low attenuation, particularly on top of a big pile of hops.