Reservations required or not and where to book?

Hi, i Will travel with some Friends in August, can you give me some advices about seats reservation?

3 August

Bologna to Innsbruck 7:45-12:36 : Seat reservation Is mandatory? Where i can book it?
Reservation is not compulsory but highly recommened  3€ per seat at oebb.at :)
For the train you have to pay a surcharge of 10€ in 2nd class or 15€ in 1st class if traveling within Italy. You can pay this surcharge and reserve the train aswell via oebb.at (Add travelers and the discount Interrail/Eurail & then single & daytickets. DONT use the Seat only option if you wanna pay the surcharge in advance.)

Innsbruck to Budapest 14:17-21:19 : Seat reservation Is mandatory? Where i can book it?
Seat reservation is not mandatory but highly recommened you can reserve aswell at oebb.at for 3€ per seat

14 August

Munchen hbf to Bologna 13:34-20:16 :Seat reservation Is mandatory? Where i can book it?
Same Condition as for the Bologna to Innsbruck train.

For all the other trains i'll take the reservation is not required. Do you advice me to book Seat reservation?
Depends on the route and traveltime but i assume this summer will be quite busy and you may reserve seats especially  as a group to get seats next to each other.

Thanks