In addition, could someone advise the most cost effective way of booking reservations, and what happens in case if delay, and the connection is missed?

The direct TGV should be running between Paris and Turin/ Milan by then, but you’d need the 0931 Eurostar. Not impossible from Newcastle, if that’s where you’re starting from, but a very early start.

You could make it a little further into Switzerland, say Lausanne (same train as the Geneva train). It’s probably a nicer place to stop for the night. Geneva isn’t the most exciting!

Another cheaper option is Paris-Strasbourg on TGV, which is cheaper than the direct train to Switzerland, then TER to Basel. Then onwards to somewhere of your choice in Switzerland for the night. This also has the benefit of being a 10 minute walk to Gare de l’Est in Paris, instead of getting across town to Gare de Lyon.

You can comfortably do Turin-Newcastle in one day with an early start, using the direct TGV to Paris. 
 

Seat 61 has the best, most up to date info in reservation cost’s and where to book them. Minimising costs means avoiding the direct high-speed trains between France and Italy + France and Switzerland, but that does show you down. The Swiss route has more options for slower, cheaper trains.

https://www.seat61.com/interrail-and-eurail-reservations.htm

To get to Milan, you could travel from Basel via Lugano and change there to a regional train across the boarder. Saves you 13€ reservation cost. Also possible to travel reservation free to Milan with a change at Domodossola but it takes longer and it’s less relaxed IMO.

Book all your train reservations on raileurope.com

Definitely agree with ralderton for Lausanne over Geneva. It’s a nicer city (albeit hilly) in my opinion - I might be slightly biased though haha

That way the early EC leaves slightly less early: departure at 06:10, rather than 05:27. On weekends you also have a much more enjoyable departure at 08:10.