This summer my family of eight will travel to Europe and visit Rome, Munich, Prague, Paris, and London. The initial plan is the use night trains from city to city except from Paris to London:

Rome to Munich
Munich to Prague
Prague to Paris

My question is how should I approach the planning and pricing of these three night trips? Eurail does not allow reservations beyond 60 days. We would much rather book in first class rather than coach. Should I consider a 5 day flexi pass or should I buy 8 tickets individually for each trip? Any help to finding the best deal would helpful.
Thanks.