If it has a start date printed on it, then no.

Yes you are. Better print some extra sheets.

You don't need to get the start date validated, but you need to fill in every journey where you use the pass as your ticket.

You can choose to either use the My Trip page that was sent together with the pass or use the My Trip-part of the Interrail app to keep track of your journeys.

You have to choose where to keep track of your journeys and once selected, the method can't be changed. 

Its train only-as the name already clearly says. A paper pas MUST have a cover and on the bottom half a page to write down trips-yes, extremely oldfashioned. I have such a thing now and on my 10th&final day using the WiFi for free of DB

@rvdborgt @mcadv 

You don't need to fill in the journeys manually in the My Trip section of the paper pass. You can choose to use the My Trip part of the app instead. The use if an outbound/inbound travel days has to be indicated on the paper pass even if the journeys are kept track of in the app.

From the Interrail website:

Recording your journey details 

Before you board each new train, bus, or ferry; you must record the details in My Trip. 

You can find the My Trip section on your Pass Cover, or you can choose to record your journeys in the Rail Planner app (and travel at the push of a button). Carefully choose which option suits you best, as you can't change your mind once you start using the Pass.

Yes, that's true but I wouldn't advise it since you can then run into the disadvantages of the app (the bugs), especially with an iPhone.

Good point

Thanks for all the info.