Train travel a 3 part question reservation and layover and trains that except the Eurail global pass

1) Yes, because A to C is a fast train which requires a reservation, while A to B and B to C are two regional trains, with more stops (and therefore take longer) which do not require reservations. The fast train probably stops in A, B and C, but the regional train from A to B stops in A, P, Q, R, S, ... and B, while the first train goes through those extra stations without stopping (and overtakes the regional train while it is stopped in R).
if you search for a train from X to Y, it will always find the quickest trains, unless you specify regional trains only.
"If I say to the train routes that do not require reservations will I have a problem arriving at C at the end of a day without a reservation?" - No. It is the train that requires the reservation, not the arrival.

But, Innsbruck --> Switzerland --> Milan --> France --> may not be the best. The quickest way from Innsbruck to Milan is south to Italy then west to Milan. Consider re-ordering this as: Innsbruck --> Milan --> Switzerland --> France --> Barcelona --> Paris
or: Innsbruck --> Milan --> Switzerland --> France/Paris --> Barcelona.

2) If the trains website shows it as a connection, then the railway company thinks you can do it. Depending on how big the station is, the minimum time they allow could be 5, 10 or 15 minutes. this is assuming you can read signs, do not get lost and are reasonably able (not in a wheelchair). If you are nervous, add 10 minutes. Some websites, including www.bahn.de allow you to add extra time.

3) Read the small print on the Eurail website. There is a page that has sub-pages for each country listing the companies and routes which do and do not accept their passes. In the particular case of Switzerland, the Eurail passes do not cover some local transport companies which Swiss railways passes do cover.

The Eurail Global Pass is what we always get. Yes, you can get from A to B and B to C without having a reservation if the Eurail site shows that there are train routes going to those places on the same day that do not require reservations but I don't understand whether you plan to actually stop and see any of the cities. Is it your plan to just ride from Austria to Switzerland on to Milan and not stop to visit any cities? That would be a great loss to you in missing the experience of enjoying the cities. We always try to allow 45 minutes to an hour for connections but that is to use the toilet and stop to eat. Eurail can show you exactly which routes are available with their pass and also help you plan your trip step by step at www.eurail.com/plan-your-trip which is a useful tool.

As Chris said, the Swiss Pass is very useful in Switzerland- www.swiss-pass.ch/en/

The Italian portion of any EuroCity train requires a seat reservation, which is included when you buy a ticket, or separate €5 per person when using a Eurail pass. On the Zurich-Milan route, the only departures that don't require reservations are those that connect to Regional trains for the Italian portion of the trip.

For most trips within Switzerland, you don't need a reservation and can just hop on with a rail pass. To know which routes don't accept Eurail passes (but do give a 25% discount), see our comparison on the Swiss Rail page. They are primarily the Zermatt-Brig-Disentis portion of the Glacier Express and from Interlaken up the Lauterbrunnen Valley to Muerren, Wengen, Jungfraujoch, etc. On the map that comes with any Eurail pass, you will see these train lines marked in a different color.

I hope that your plan is to make a few stops in France. If not, then I would fly to and from Barcelona and your rail pass equation would be quite different. If you do use a rail pass in France, you need to reserve those trains further ahead, while Italian trains have no deadline or artificial limitation on seats for pass holders.

Thanks for the replies, all of them have great information, exactly the kind of information and guidance I was hoping for. Last night we were focusing on the portion of the trip to Milan where we will spend 3 nights, then 1 night in Nice, 1 night in Marseille, 2 nights in Barcelona, 1 night in Carcassonne, then on to Paris for 4 nights, this is after a Rick Steves Best of Germany, Switzerland and Austria tour. We will dawdle as long as we can, we are leaving most of Italy and Spain for another trip. While in Milan we also were planning to take the train to Lake Como for the day. Any further information regarding reservations and rail travel in Italy, France and Spain are greatly appreciated. As suggested, lunch at a cafe in Zurich between trains sounds like a great Idea, people have to eat.

The only way to get to Lake Como on a Eurail Pass is to go to Como San Giovanni station on the mainline Trenitalia track. This station is a long walk from the lake in the town of Como. Another railway company, Trenord, has a station right by the lake, but they do not accept railpasses. Further, the Town of Como is not the most desirable spot to visit Lake Como. Better would be Varenna, in the middle of the lake and one of its most scenic areas. Again, it is served by Trenord. The bad news is they don't take Eurail Passes. The good news, it is only 6.70 euro per person each way for the one hour journey.
Another lake option is Lake Maggiore at the town of Stresa, which is OK with a Eurail Pass. Just as nice as Como with some interesting islands reached by a short ferry ride.

Edit- As for as lunch in Zurich, I'd skip it and travel to Milan via Verona as previously suggested. Its the fastest route, has some great scenery over the Brenner Pass and down the Adige valley, and you can travel as far as Verona on unreserved local trains. Verona would make in interesting stop for a couple of hours with lunch on the Piazza Bra overlooking the Roman amphitheater. Then a reserved fast train to Milan.
You've already done Switzerland on your tour.

Eurail Passes are about as useful as Traveler's Cheques these days...they've both gone the way of the dinosaur. Just buy point to point tickets and don't worry about where your Eurail pass is accepted.

This does not exactly pertain to you since you're not going to Germany. I use a rail Pass and it's valid everywhere in Germany....almost. Those cities served by a regional train line, esp the more remote places in the eastern Germany, I ask at the station. If there's no one to ask, I buy the point to point ticket saving my Pass for another day when I'm riding the ICE. So far, the regional trains I've taken in western Germany not part of DB, my Pass was accepted, whether the controller was correct or not, I don't know. I've never been told on a non DB regional train that the rail Pass was not valid.