Passes can be bought and used almost instantly.

You can search for (and buy) reservations before buying a pass.

There are only a small number of routes where you will have difficulty getting reservations a week or two in advance, if you say where you plan on going we can give advice.

As you are from UK then the most likely to be a problem is Eurostar across the channel as this does get booked out.

My itinerary and dates are flexible but my preferred destinations from London is Amsterdam or straight to Zurich via Strasbourg, Germany, Vienna and ending my trip in Istanbul by 17th august. I dont mind which country first to hop into or whichever station that will let me get on in Eurostar. Or if theres an alternative to Eurostar as long as i can get out of London.

Any inputs please. Thanks!

You can check and book passholder reservations on Eurostar through this link

https://www.b-europe.com/EN/Booking/Pass

You will need to use this to book

If you can’t find direct trains to Amsterdam search for Brussels instead where there are more trains, from Brussels to Amsterdam there is the hourly IC service that needs no reservations.

Use this for high speed trains in France

https://travel.b-europe.com/Eurail-GE/en/booking-tgv#TravelWish

The international TGV trains have expensive reservations, especially the Paris - Switzerland route, it can save money to take TGV to Mulhouse or Strasbourg and change for regional trains from there.

For travel to Istanbul this website should be read carefully https://www.seat61.com/Turkey.htm

It shouldn't be an issue then ! For example :

- London - Amsterdam 08:16 - 13:13 35€ on 3rd August

And plenty more trains by changing to the hourly reservation-free IC in Brussels. Check availability here : https://www.b-europe.com/EN/Booking/Pass#TravelWish

ICE trains from Amsterdam to Germany require seat reservations this summer, 3€ on tickets.oebb.at. If they're full there are multiple regional trains crossing the border.

There are also night trains between Amsterdam and Zurich, Zurich and Vienna. They're very popular so check availability on nightjet.com (add Interrail as a discount). The journey can of course also be done on daytime trains (reservations optional but recommended in summer).

Btw you can buy passes on myinterrail.co.uk to save a few £

Thank you so much!! I can feel all the cells in my body jumping with excitement ready to embark on this new experience!!! 

Do not hesitate to come back for questions. I'm sure that you'll enjoy your trip ! :)

Will the 10days-2 months  global pass enough for the above mentioned itinerary? And is it worth buying a First Class ticket? Does it makes a difference when making seats reservation for 1 adult and 1 youth? 

Thank you!

Yup 10 days should be plenty enough but you know how many stops you're planning.

I'd say that 1st class is worth the cost as seats are comfier and carriages are less crowded (main pros). The price difference is also smaller with a pass than with regular tickets.

You also get free seat reservations in Germany (incl. ICE from Amsterdam), Austria, Hungary through ÖBB.

Eurostar is a bit more expensive in 1st (8€ more I think) but you get a small meal.

Hi, finally bought the global pass, thank you for your help! But being new, still dont know what im doing. So i managed to book and pay the Eurostar reservation thru the SNBC app using the above link. So my trip details is in that app. How do i put that booking in the Interrail Planner app? And…

For my first outbound journey using the local train to get to Eurostar, do i need to book it? How? If not, do i just hop on the train? What will i show the inspector as i dont have barcode.or something for my global pass.

Thanks in advance for the guidance

You just have to add trip n your rail planner. The reservation you show separately on check in.

which local train exactly are you planning to use? Usually you can just board them.

the barcode will appear when you add it to your trip in the rail planner.

I tried adding on the Rail planner the domestic train via Thameslink (from my home to london) attacched photo.

What did i do wrong? I have already added on the Rail Planner the London-Rotterdam reservation.

Please help. 

Probably you have to add that train manually. Some trains are not shown in the railplanner app and need to be added manually.

You'll find those trains if you choose "London” (without any specific station) as the destination.

I have not activated my pass yet.. someone mentioned a barcode will appear? But im not seeing a barcode in My Trips? The London-Rotterdam trip is already reservee but the barcode is on the Eurostsr app. Is "my trip" on the Rail Planner wrong?

After activation, a slider will appear after each journey in My Trip. If you tap on it, then the journey will be added to your pass. If you then go to My Pass, you will have a button "Show ticket”, which will show the QR code and below it the trains you have added to your pass for that day.

Alse see:

https://www.interrail.eu/en/interrail-passes/interrail-mobile-pass/getting-started

Am i correct to assume that with my Interrail Pass i can hop onboard anytime on any domestic train in any country i am in? Do i need to add all domestic train in the Rail planner all the time and connect the Interrail pass? 

On the above photo of My Trips, do i need to add all the trains i am going to use when reaching Rotterdam? And when is the best time to activate it if i start my very first journey at 3am on 3rd august? 

Yes you can use any train of any participating operator. And you need to add all trains you use to your pass.

On the 3rd, just before boarding. You should never activate anything in advance, since you can't cancel activation anymore when validity has started.

For any subsequent trains on the same day, it doesn't really matter when you add them, since they don't use an extra travel day. The only requirement is that you add them before boarding.

Thank you ever so much @rvdborgt and other travellers for all your kind assistance in a matter of writing, much appreciated! 

p.s i will be coming back here until i figure this Interrailing out, meanwhile relying on other travellers tips and advice