9lb maris otter
1lb caramel 40 (for head retention mainly)
East Kent Goldings hops with the following additions
.5oz 60min
.5oz 30min
.5oz 15min
.5oz 5min
As a style it's all about balance and sessionability. 40IBU is a bit on the high side - I'd aim for 30-35 IBU. However you need to bear in mind that at this time of year, your hops will have lost a lot of alpha. Depending on how they've been stored the EKG could have lost anything from 30% to 60% of their alpha compared to fresh - and their aromatics will probably tell a similar story. They're not as bad as varieties like Cascade, but they don't keep particularly well. So you need to allow for that, even though it's a bit of a crapshoot guessing how they've been stored unless you've kept them since harvest.
It's also worth bearing in mind that British hops show significant vintage variation, unlike hops grown in irrigated desert like Yakima. 2016 was a pretty poor vintage, particularly in East Kent, whereas 2015 was a great vintage. Unfortunately it's barely worth the extra year of storage - I guess if you really want to see what EKG is really about, you might want to wait until the new harvest in a few weeks time.
However, that doesn't really help you now. If you wanted something British, then something from last year's crop in Herefordshire would probably be better than Kent, but few hop merchants even in the UK go to that amount of detail (except for Goldings). But something like Challenger is a classic and widely grown, I've got a packet of Bramling Cross waiting for a single-hop bitter. BX is possibly my favourite English hop, and it's a bit less subtle than some so may suit US tastes, without exactly being shouty. A more left-field option is Flyer, which is a new hop that is probably more suited to darker beers, it's on my list to try.
I'm trying to do more single-ish hop beers myself to learn my way round their flavours, since we normally get them in 100g packs here I'm tending towards 20IBU of something else to bitter at 60 min, and then use the whole pack of test hop split 40-20-40 at 5-min, whirlpool, dry-hop. Or something like that, I haven't quite settled on it yet. Doing a more complicated schedule like yours will undoubtedly produce a more complex beer, but for these purposes a simple schedule is good enough - and I'm more likely to do it consistently between batches!
I do think you want to be adding significant amounts on the cool side, either in whirlpool or dry hopping, to see what aroma compounds are there in your hop.
A classic English bitter these days would probably be Maris Otter with mebbe 5-8% crystal 80 for sweetness and 2-5% torrified wheat for head. But if the caramel 40 is what you can get then no worries -I can understand wanting to keep things fairly simple and similar across different beers. I'd probably mash a wee bit warmer, maybe 153F to maximise long-chain dextrins.
Do you know what your water profile looks like? I wouldn't go for the full Burton, but half a teaspoon of gypsum wouldn't hurt.
If boilovers are a problem, you need some simet(h)icone - FermCap or a variety of stomach gas medicines.
And obviously don't overdo the carbonation - 1.5-2 volumes CO2 is plenty, and serve at 55F rather than fridge cold.
