Welcome!

1. Yes, you can expect prices to rise annually with inflation. I’m not sure exactly when the price rises will be, but quite probably before April. So if you buy now, you can avoid the price rise. There’s often a sale during the end of November, so keep an eye open for that discount.
2. Don’t use the Eurail app or website for planning, the timetables are often out of date. Try searching on bahn.com/en which is much more up to date
3. As above, the Eurail timetable isn’t always up to date
4. You can make reservations without activating the pass. You have to add all trains to your app before you travel, but it doesn’t need to be done far in advance.
5. Really good info here: https://www.seat61.com/interrail-and-eurail-reservations.htm
6. Yes, read that page on Seat61, and this one, which explains the pass really well. Post your itinerary here, and other travellers can help you with any specific questions/ problems  https://www.seat61.com/how-to-use-a-eurail-pass.htm

Frankfurt - Amsterdam
Yes, DB is good. Avoid Eurostar if possible, because they charge expensive reservation costs.

Amsterdam - Brussels
Again, avoid Eurostar. There’s a good Intercity service, which is slightly slower

Brussels - Paris
You probably need to use Eurostar on this route. The alternative (if you’re travelling with a Eurail pass) is much slower and indirect.

Paris - Bern
Option 1: Direct TGV to Basel, then Swiss trains to Bern. Quite an expensive reservation cost, but fastest.

Option 2: TGV to Strasbourg or Mulhouse then TER to Basel then Swiss trains. Cheaper, because you only have to pay for the domestic TGV reservation, but slower.

You should be able to find all these routes by searching on bahn.com/en. Let us know if you have any problems.

Paris - Bern also has a few options via Frasne. Also with the cheaper domestic TGV reservation.

Thanks everyone for helping me out.

1. As mentioned about Black Friday sale - when this is coming out? and is it FCFS basis?
2. My routes on EU Rail planner website shows no reservations for Frankfurt to Netherlands, Netherlands to Brussels and Bern to Salzburg. 
3. Only reservations are showing for Brussels to Paris and Paris to Bern as you guys mentioned this is one of expensive route and I can take alternatives but they are longer, I will look into it once I have purchased the pass.
4.  To confirm - EU rail pass covers all Inter City trains in Netherlands (Zaandam, Giethoorn, Amsterdam etc), Belgium (Bruges, Ghent), Switzerland (Interlaken, Lauterbrunnen, Brienz, Zermatt etc ), Austria (Salzburg, Innsbruck, Hallstat etc) as I can see these routes are coming on EU planner website under EU rail pass and I assume all these trains are covered under EU rail pass
5. Also any suggestions if Bernina express is best one to cover as I see its only closest to Bern I am staying and I can cover it from Zweisimmen to Montreux and come back via intercity from Montreux to Bern. I see this is fully covered under EU rail pass except I need to book reservation with small fee?