There are reservation fees but for domestic trains in those 3 countries they are not mandatory.

In Germany and Austria it may be a good idea to reserve on long distance IC/ICE/Railjet as they can be quite busy.

Switzerland it really is not necessary to book any domestic trains.

Seats on night trains are sometimes non compulsory but due to the lower capacity it is recommended to reserve them, sleeper/couchette berths and cabins need to be reserved, they generally sell out well in advance.

Fees for seat reservations in those countries are not high, generally less than €5, it does depend on where you book.

Outbound/inbound means you have 2 days as part of the validity of your pass (they are not extra days) in which you can travel in your home country as well as anywhere else. You do not have to use them and can choose to use them at any point within the pass validity.

Here is some useful information from the experienced travellers in the Community regarding both planning, reservations and activation of pass and travel days. 

 Planning

The rail planner is normally not up to date, as it only is updated once a month, so to be sure of the time table you better check the timetable and availability on the websites of the national railways. The bigger national railways, like DB (Germany) SBB (Switzerland) and ÖBB (Austria) cover several countries. 

 Reservations 

The advice from the experienced travellers in the community is to use other ways to make reservations than the Interrail/Eurail website.  You can look at the guide in the link:

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105

If you, after having looked at the guide, have questions about how to make specific reservation, please give your travel details (departure date, time and route) preferably in a new topic, and you will get advice.

Please note that Interrail/Eurail charges an extra fee of 2 EUR per person and train in addition to the fee for the seat reservation.

 Activation of pass

During the activation process, when you choose the start day of the validity of the pass, the first day of the validity period is automatically made a travel day, even if you don't enter a journey, the advice is therefore not to activate the pass before the first travel day as you only can deactivate the pass before 00.00 on the day the validity starts. If your travel plans change in the last moment you will loose travel days if you have activated the pass in advance.

It can be wise to make a test and activate the pass with a start date well in the future and then deactivate the pass immediately, just to see that everything works.

 Activation of travel day

The advice from the experienced travellers in the community is also never to activate a travel day, that is connect a journey to your pass and create the QR code, until just before boarding the train, otherwise you might loose a travel day if your travel plans change in a late stage  You can't delete a travel day in the past. A travel day can only be deleted until 23.59 CET the day before the travel day.

NightJet trains-organised by OeBB from Austria, must all be REServed and cost a fair lot extra-even for a seat 14€. There are not that many nighttrains left in these countries. But in DE=Germania DB also has a few daytime trains=seats only (ICE)_ that run overnight and you can use for ´free´-you can RES if wanted directly via bahn.com - option seat only- for 4,50. You can even do that on some machines of DB INside DE, but then you have to know how to set up-it is not very obvious.

Choosing a specific seat is usually not really possible-you can, maybe, choose between aisle/window, or -if they have it- special compartments-silence or family. IF you really want that, visit a CD-special counter in big cities (probably not Prostejov) where they MAY be able to help you. Sometimes railway staff-those who know how to handle it-not anyone will- can get more out of the systems as we normals.

BTW-another Cesky posted a few weeks ago that IF you want to make more trip-return do vas dumy=home in between, CD sells special --to border´ tickets for passholders for just 35kr.

Yes, the OUT+IN will cover the whole route dum-hranica. BUT only on CD- RegioJet and GW-trains do not accept passes (RJ only on some lines that they now run on contract).

I am now also on a pass and last sunday was in Trutnov, where there was even a ´den zeleznice´-of whcih I had no idea.

Please check first before you write something. As far as I can see, RegioJet accept Interrail on all their trains, except for the train Prague - Rijeka/Split.