Critique my first partial mash stout

I'm making a partial mash Sweet Stout, and am a bit confused about how much of the darker grains and sugar additions are appropriate. My goal is a very full, creamy mouthfeel. This is the evolution of an extract-only stout I made that was good but way too thin.

This is my recipe in Brewtarget. Note that it doesn't account for unfermentable sugars, and that I'm going for a high mash temperature, so I expect FG to be higher and ABV to be lower. Mashing/sparging in a grain bag in a 4 gallon cooler, so I'm assuming a low efficiency.

Batch Size: 5.500 gal
Boil Size: 3.000 gal
Boil Time: 1.000 hr
Efficiency: 60%
OG: 1.060
FG: 1.012
ABV: 6.2%
Bitterness: 25.9 IBUs (Tinseth)
Color: 37 SRM (Mosher)
Mash thickness: 1.4 qt/lb

Fermentables
3.5 lb - Maris Otter
1.0 lb - Caramel/Crystal Malt - 60L
1.0 lb - Chocolate Malt (US)
0.5 lb - Barley, Flaked
0.5 lb - Roasted Barley
0.5 lb - Milk Sugar (Lactose)
0.5 lb - Maltodextrin
5.0 lb - Extra Light Dry Extract

Hops
0.6 oz - Chinook 13.6% (1 hr)

Misc
0.5 tsp - Whirlfloc
0.5 tsp - Yeast Nutrient
4.0 oz - Cocoa powder

Yeast
Danstar - Nottingham Ale Dry

Mash
Mash Infusion 2.275 gal 158.000 F 1.000 hr
Final Batch Sparge Infusion 1.820 gal 165.200 F 15.000 min


My reasonings were:
* Maris Otter base for enzymes (28% of fermentables)
* Crystal 60 for enzymes, flavor and color (8%)
* Chocolate malt for flavor and color (8%)
* Flaked barley for head and protein body (4%)
* Roast barley for flavor (4%)
* Lactose for sweetness and sugar body (4%)
* Maltodextrin for sugar body (4%)
* High mash temp for increased unfermentables
* Reduced amount of grain to decrease mash thickness for increased unfermentables

How does this sound. Did I go overboard anywhere?

You might be a bit heavy on the dark malt for a sweet stout (I'd drop mhalf the chocolate assuming your roasted barley is the ~500L type), but otherwise it looks solid to me. I might also back down on the bitterness (and use a mellower hop), but that is up to you. Hope it turns out well, good luck.