Indeed, we already met on the road :-)

As promised, some more information below. You will also find some pics on twitter @TLyagushka

Maps: I have not come across any paper map that is even remotely useful. The large scale Michelin has no detail, Reiseknowhow Kenya is rubbish in the area, and two other brands I looked at in Nairobi were also completely wrong. If you are going North, JJs has a relatively accurate map with comments on the living room wall. T4A is mostly spot on though, and I would highly recommend it. Only between Park HQ and Loyangalani the last 35km before Loyangalani I didnt match what I saw.

Fuel: last fuel pumps with 95% chance of finding fuel are Arba Minch and Jinka, although both were out of fuel when I was there. In Kenya reliable fuel is available in Maralal. In between there may well be black market fuel, amongst others in Konso, Weyto, Turmi, Iliret and Loyangalani, but I wouldn't bank on it. If you want to make life easier for yourself, try to be in Arba Minch Fri/Sat when many Tour Landcruisers start heading for Turmi/bulljumping. If you are lucky you can find a group that will also visit Omorate, and may take some fuel along for you. I did exactly that and could start in Omorate with 60L total. Try to avoid the black market fuel in Ethiopia if you can, its between 1.5-3x regular prices and has even more gunk in it than the fuel at the pumps. 60L were too much, and I jettisoned some fuel along the way. PM me if you are taking this route, there may be 7.5L available in Sibiloi (but don't bank on it).

Water: available everywhere where you might get fuel, plus at Hado (and several villages north of Banya from pumps), Koobi Fora, Sibiloi HQ. Don't underestimate water consumption, with the wind and heat it can be well north of 8L a day. Plus you need spare in case you get into trouble, enough for 1day wait + to potentially walk out. I'd recommend taking rehydration salts, made a big difference for me at close to 50C.

Road conditions: likely to change daily, and rain will change everything, so take the below only as an indication. Also bear in mind that I am on a 148kg bike with minimal luggage and good suspension. Expect everything from soft sands, gravel, lava fields to large rocks on slopes. All easily doable on a dirt bike with your mates if you have offroad experience (not just green lanes or pistes!). But luggage, heat etc it could turn into a nightmare. Most memorable bits for me were the famous rocky hill some 20km north of Koobi Fora, ridiculously deep sand around Koobi Fora, and strong gales on rocky slopes south of Loyangalani.

Route options: I hear different opinions whether the route through the park or the one around is better. I took the route through the park, with Koobi Fora as a rest place. 22km south of Park HQ is a junction, I took the western route along the lake, which is very likely in much worse condition than the eastern route via North Horr. In particular, on the western route, the last 35km into Loyangalani were very sandy, and this is also were the track disappeared and T4A failed me. I went along the lake shore all the way in the end. Beautiful, but harder than the other option.

Riding times: take only as indication. I was going relatively slow, as I was solo and didnt want to risk broken limbs or smashed engine cases on the rocks. Changing tracks, rain and your bike/ability also factor in this of course. Also I generally started at dawn and called it quits by noon at the latest to avoid the heat.
Omorate - Iliret approx 2.5h (Day 1)
Iliret - Koobi Fora approx 3h (Day 1)
Koobi Fora - Park HQ aporox 3.5h (Day 2)
Park Hq - Loyangalani approx 7h (Day 3)
If you are an experienced offroad racer *and* have a recovery vehicle you could probably half the above times, if you are new to the game and have a heavy bike, you'll probably be looking at double. Time is critical in so far as water = time, and concentration will deteriorate in the heat ...

Accomodation: camping, rooms, showers etc are available at Koobi Fora, so long as its not the archeologists convention the day you go. If coming south, I would strongly recommend not camping at park HQ as $15 for zero facilities is ridiculous. Loot cold drinks at their canteen, and then set up camp just outside the park. In Loyangalani, I found the Palm Shades Camp nice. Depending on your luck, Koobi Fora and park HQ may or may not have food.

Immigration: as laid out above by Wazungu, except I didn't ask for the FPV disc nor roadtax, and neither was ever asked of me. I did exit via a bush border though, it may be different at larger crossings.