Your Biscuit may get lost but won't hurt. I'd throw in a fair measure of flaked barley for body and head retention. When I've done similar beers, the IBUs are closer to 40 and it works out just about right.

 

Not to be a bugger bit I was going to suggest flaked oats but I'm being a PITA. On first glance at your recipie I thought tasty the marris other base and biscuit should give some lovely depth and the flaked barley should give some nice body/mouthfeel. I see your aiming for a balanced profile playing it safe there for a first pass good ideah I'd do the same.

 

Don't see any reason it wouldn't be quite good. Irish Stouts tend to be crisp and dry so I'd keep the mash temp relatively low if you intend a single infusion.

 

You could swap the black malt with chocolate malt for a more chocolate flavored beer. Other wise it looks good as is.