Definitely put me in the *high five* camp. Go for it! Right now, I think I'd need $100k to do that trip, but I also remember a time when I would have said $24k/yr = $2k/mo = $60/day....yeah, I can do that!
Now on to my own less/more recommendations:
- 2 weeks of Turkey: this actually could be about right, it just wouldn't be all in Istanbul. Lots of archaeology, nature, beach, etc. in Turkey.
- 10 weeks of Central America feels very long. 20% of your trip right there...I'd probably knock that down to a couple weeks of Belize and Costa Rica. I'd skip Cancun unless you're solely there for some of the nearby Mayan sites: Cancun itself is a tourist trap. Take 6-8 weeks of this time and distribute it among South America and Southeast Asia.
- I've never been to Iceland, but everybody tells me it's heaven and I'd want more than 3 days there.
- I'd definitely shift Europe to Sept/Oct (or to the start of your trip - April/May), especially if you want to hit the hostels, pensiones, and Airbnb spots popular with backpackers.
- I don't have any problem with 2-3 days in CAI. You'd have a full pyramid day, a museum day, and your going/coming day. If you do this, hit Giza right when it opens and then get the hell out of there when the bus tours roll up. Go down to Saqqara and Dahshur in the afternoon...we did this and had the entire North Pyramid to ourselves. A more extensive Egyptian trip would include Luxor, Aswan, and Abu Simbel...if you're *really* into Egypt. That would be 7-10 days.
- Maybe consider a couple weeks of Isreal/Jordan.
- I'd allot a lot of time to Southeast Asia because there are so many different experiences to be had there. More than anywhere else, this is where I think you'd be likely to throw in an unplanned extension or ad-hoc modification to your trip. I think this is where I'd earmark some of those Central America weeks...
- Any thought given to more of Africa (beyond Egypt)?
- Maybe work a little Nepal/Bhutan into that 2 months allocated to India. 1 week of each would be enough to do some amateur (guided) trekking. 3-4 weeks are needed to do serious altitude trekking. (Higher altitude treks also get expensive.) With or without trekking, these are absolutely fascinating places.