Brewing my first partial mash

I've brewed my first extract beer and it turned ok but nothing like i planned, after tips from other brewers i undestood what i did wrong, now i'm thinking about the second beer and i was told that a brown ale is the sefest taste wise and easiest, i'm more of a porter/stout guy so i went toward that direction, i came up with a simple recipe, i want to know if i'm in the right direction, i don't want it to be too roasty, too thin or just plain unbalanced.

the bach is 20 liters:
1.5 kilogram Muntons extra light DEM
1.5 kilogram Muntons light DEM
0.5 kilogram Muntons amber DEM
0.5 kilogram Muntons wheat DEM
530 grams of oatmeal concentrate
grains:
235 gram Weyermann cararoma(dark crystal)
235 gram Weyermann carafa type 1(chocolate malt)
mash them for 30 min. in 155 degrees.
boil:
70 min.
hops:
E.kent golding
30 grams for 65 min.
30 grams for 45 min.
20 grams for 25 min.
20 grams for 5 min.
20 grams for dry hopping in the first fermentation.

yeast: S-04.

150 grams of coca nibs in the second fermentation( should i roast them of sanitation or are they fine as there is).

first fermentation: 10 days.
second fermentation: 20 days.
botteling for 14 days.

Your thoughts on the recipe.

thanks.

the grains you've chosen can't convert themselves. so this isn't a partial mash, just an extract with steeping grains.

If I were you, I'd go to the recipe database on this site, and start with an existing partial mash recipe. There's A LOT of variables when you start mashing grains, and can be a bit to wrap your head around at first. Seeing a proven recipe (especially posted by one of the long time members here) is going to help clear up some problems right away.