Just back from overland trip to Nepal on this route so hopefully this will give you some info -
From the RAC, deposit for your route is 500% of bike value. Couple of options such as bank guarantee or insurance policy. We went the insurance route which costs 10% of the deposit value but after the trip you get half of that back. Which route works best for you will depend if you have the money in the bank, how much your bike is worth, etc
Didn't need a visa for Turkey
in advance and in fact it was cheaper to buy at the border than in advance. Just be aware you need to pay the visa in Euro and the guy behind the counter was not interested in Euro coins (wanted notes). We ended up paying in Turkish Lira because of this but did not know the exchange rate in advance and ended up giving him a healthy commission...
visa was straightforward like you say, just filled out the forms.
visa we used visa agency persianvoyages.com. Narsin over there basically gets you a pre-authorisation number from Tehran which you take to your elected Iranian embassy (note this could be along your way - not just at home) and use to get the visa. With this route we had Iranian visa same day at the embassy. (Iran is superb)
visa is more difficult, esp if you tell them you are coming by bike apparently. We simply didn't mention it and they never asked. With us the embassy changed the application form we had to fill in AFTER we had submitted the first version and never bothered to tell us. We chased them over the phone etc but ended up doing a 200 mile round trip to see them in person. This was definately a good decision as we eventually had it sorted on the same day. You need a letter of invitation from someone in the country and I think bank statement etc. Once the commissioner saw our LOI he seemed happy enough. Real pain was the entry had to be within 3 months for 1 month stay, putting time constraint on Europe and Iran and meaning you have to apply as you are about to leave. Also not possible to get Pak visa outside home country apparently.
Watch out for 80Euro insurance to go via Serbia if you are thinking of it. Roads are pretty good but maybe Romania would have been cheaper.
It is possible to get insurance in India for around £10 and probably a good idea. There is always an argument about whether it would be valid for some bureaucratic reason but at least it shows you have tried. With the driving in India there is every chance of a minor bump possibly turning into awkward questions if you don't have it.
Watch out for fixers trying it on to sell you insurance at the border from Turkey to Iran (at the Iran side, last gate approx 1km from the initial customs house at the border). It should cost around 18 Eur for a bike. There is a thread about it on here somewhere although some folks recently went through with no issue (this is at Dogubayazit)
What pecha says about India is absolutely spot on. I'm glad to see someone else say it - makes me feel less of a wimp
. Best to take it very easy through India, don't expect to do more than 60 miles a day, 100 if you are very lucky. The golden temple in Amritsar is a must-see though.
Ship out of Nepal rather than India (airfreight). From what I am told India is a pain to ship out of wheras we found it pretty easy in Nepal. Its also a great country you really shouldn't miss while you are out there with friendly people and fantastic scenery. We used Eagle Exports in the heart of Thamel, Kathmandu. Suraj and his wife are really friendly and sorted out everything. His details are also on here someplace, drop him an email for a quote.
Any other questions I can help with drop me a line. I'm sure you'll have a great time.