An ICO is a rally dedicated odometer which can be adjusted plus / minus when you miss turns and have to readjust the mileage. If this is your first rally you will be doing that quite a lot, no offense
Plus, as all rallys in greece (and Albania and Sardegna) have quite "dense" navigation instructions, you will be needing the second decimal in your ICO (the one that counts in tens of meters as opposed just the one decimal that counts every 100 meters). Not sure if the stock odo does that.
No need for two, one ICO + your stock odo for checking your speed on speed limit zones should be enough.
You'll have to factor in the sensor bracket (pick up) to your costs, a spare sensor cable. These can sometimes go boom on rocky trails, hence people using two ICOs side by side. If one fails, they keep going with the second. Without a working ICO, you are lost and up shit creek. (Of course you could always whip out your GPS, but asking for the tracks from the organizer will most probably disqualify you from points in the Roadbook class)
I would suggest an electronic roadbook, twisting knobs on a manual while dealing with rocky trails and lots of sinuous mountain roads with drop-offs is no fun & could be dangerous.
Look around for used ones, the organizer of Hellas Rally is also the Touratech importer, hint hint. Drop him an email, he should have a bunch lying around, plus controls.
Plus: a larger tank. MInimum range for HR is 150kms. This being your first rally, factor in getting lost, you will need a range of up to 200kms
I would also fit some sort of steering damper. As I said the route will probably include a bunch of rocky terrain. It might be a luxury and a damper helps save energy instead of wrestling with the bars all day. PLus the prologue will most probably be on sand, and it always helps to get a good seeding position for the second day which will be the first of the long ones. A damper will help a lot in the sand.
Hellas Rally is a good one to choose for your first rally, it's pretty laid back, lots of people go just to have fun and you'll only see 20-30 riders really competing for times. The only problem with taking a too laid back approach is when the quads and cars catch up / pass you. Dusty as hell and a pain in the neck to pass. Try and keep a good rhythm going and set a target for each day (ie. top 50% of bikes or something like that)
See you there!