Kinesis Aithein - disc brak r def

So my brother has decided he's going to do an Olympic triathlon soon and wants to do some road cycling as well. He started sending me links to rather expensive and fancy bikes, but being a thrifty man, I poo-pooed that idea and had a quick peek on here. I immediately spotted @macaroon's Kinesis Aithein for sale thread.

I'm a big fan of my 4S disc and really like the look of the Aithein, so suggested it'd be a good choice and it looked to be about the right size for him, he's 6'4" and it's a 59cm (if it works for Bruce Dalton...). One thing that macaroon noted was that there's only enough steerer for a completely slammed stem. Should look good and my bro's young enough to still be flexible.

So the plan is for a bright orange 59cm frame, slammed, with plenty of seatpost and all parts black. I'm hoping it'll look pretty good.

So, with macaroon getting the frame in the post and my brother telling me he was completely uninterested in picking parts for it (apart from deep carbon wheels, he definitely wants those), he left me to piece together parts and work out a build.

As I mentioned previously, I'm a thrifty man and feel especially responsible about not buying him anything too shit, but also not pissing away his money needlessly.

With that in mind, the purchased parts list looks like this, so far:

Kinesis Aithein 59cm
Cosine 24mm cheapo wheels
Vittoria Rubino 3 folding 25c tyres
Deda RHM02 bars (44cm)
Deda bar tape (black)
Pro Tharsis alloy seatpost (placeholder until we work out fit, cheapest 31.6 post I could find)

Still to buy:
Shimano 105 5800 groupset
Stem (dunno, I've got a few spares kicking around so we'll see what fits him. Long-term, probably a black on black Deda)
Saddle (dunno, something from the parts box to start with - I've got a black Romin Evo Expert lying around)
CN*carbon 50mm clinchers of some kind.

What else am I missing? Anything else I'll need?