Taking cue from t_maia, if you're considering going directly from Barcelona to Switzerland, Elipsos night trainhotel may be the way to go if you don't want to lose too much time. Just plugging in a random search for travel in January, the timetable (which may be subject to changes) shows departure from Barcelona at 7.38pm and arrival at various Swizz cities the next day would be: Geneva (5.45am), Lausanne (6.54am), Fribourg (7.46am), Bern (8.49am), and Zurich (10.07). It's a single journey without train changes, making it quite convenient.
Nomadic Matt recently wrote an article of his opinion if getting an Eurail pass is of good value. Have a read.
Another option you could consider, for inter-European countries travel, is travel by bus (i.e. the Eurolines). Say, if you plan to stop in South of France, there are limited train options and you may even need to look into booking trains separately, e.g. Barcelona to Perpignan (3-4 hours), then Perpignan to Marseille (4-5 hours). These short train rides would usually be done by day, so you could potentially lose quite a lot of time for the rail travel. But Eurolines would have a bus leaving at near midnight from Barcelona and arrive in Marseille at near to 9am the next morning. So similar travelling time, but overnight, and bus is usually cheaper than train too. The strategy with Eurolines is to buy your ticket ahead of travel, as there's usually a discounted price on the web.
Re spending money, assuming the flights and train tickets/passes etc have been taken care of, t_maia has already given a good indicator of how much you would need for accommodation, food, local transportation and some sightseeing. Do remember that Switzerland is going to be expensive, whereas Spain and Portugal would be cheaper, with France somewhere in between, so your daily need in the different countries will vary. I'd guestimate €40-€50 per day for Portugal/Spain, €50-€60 per day for France, and a good €70 per day for Switzerland. This should allow you to travel in reasonable comfort. I don't particularly like thinking in terms of what's the absolute minimum I can get away with because it means constant worry on the budget, but to allow a bit more wiggle room with some extra allocations, it's always nice if there are extra unused money left. (But that's just me) 
In terms of accommodation costs, in Portugal, e.g. Lisbon - you can get dorm beds in very good hostel (say the ones that won HostelWorld best hostel awards last year) for about €16-€18 euro pp/pn. In Spain, Seville's rate for hostel varies between €12-€15 pp/pn. For Barcelona, it'll be similar to the prices in Lisbon. When it comes to Marseille in France though, now it'll be about €25-€30 but they tend to be private rooms rather than dorm beds. Next up, Switzerland, e.g. in Bern, the price of €25-€30 is now for a dorm bed. To reduce your accommodation costs, you may look into couchsurfing. And for one stop hostel booking website, I normally use HostelWorld.
Bearing in mind the estimate of spending money, food will inevitably be common day-to-day items and no fancy restaurant eating. There's usually cooking facilities in hostels so you can buy stuff for cooking from a local supermarket. However, do look out for local foods and some of them do come at reasonable prices, e.g. tapas in Spain can often come by for about €10 per person. Eating out at lunch time will also be cheaper than at dinner, which works quite nicely since you'll be out and about at that time, and can get the food as you go along. In the evening, you'll be back at the hostel, which makes the possibility of cooking more likely. Or, check the hostel notice board - often there could be special nights organised for group outing where it won't cost too much to eat out etc.
