Acohen,
I've run the Edinburgh Marathon the previous 3 years, and will be ther again this May.
You needn't have any worries. This is a flat, friendly, well-orgnised race with all of the best facilities you will need. I haven't checked out the course profile for this year (and the website isn't link properly

), but I imagine it will be the same as last year. The start is pretty obvious - in Princes Street in the centre of town. You won;t be able to miss it. And if you get lost just ask someone for directions - Scottish people are very friendly and helpful.
I don't believe you will be taken to the end if you fail to finish. There are many marshalls on the route. So, I am sure they will advise a happy ending if you need to get back to the city centre.
At the finish I would advise taking a mobile phone to contact friends. Leave it with your bag at the start and you will be able to collect it at the end. Otherwise you may not fine your friends. I suggest following everyone else to the bus stop and returning to Edinbugh cityy centre - make sure you have some money.
Just remeber, Edinburgh is one of the best marathons. Have fun and enjoy.
S.