Time frame for secondary

Here's the recipe:

5 lbs Dark Extract (Liquid)
2 lbs Pale Extract (Liquid)
1/2 lbs Malto Dextrin

3/4 lbs Chocolate grains (steeped)
1/4 lbs Crystal 40L (steeped)
1/8 lbs Black Barley (stepped)
1/8 lbs Black Patent (steeped)

1 oz Galena (60 mins)

White Labs London Ale WLP013

At bottling, 1oz Unsweetened Baking Cocoa

Click to expand...

Couple of questions ..
I racked to secondary 4 days into fermentation. It was once the krausen subsided and another day to let it clear a little. I'm planning on leaving this in the secondary for about a month. Is that going to be to much time?

If I'm going to let it age that long in secondary, should I rack again to get it off of a potentially nasty yeast cake?

Am I going to benefit from letting it age this long in the first place?

A month won't be too long for that big a stout. I'd say you moved it a little too soon (I leave big ales in the primary for at least a week), so plan on racking it again in two weeks.