I've stayed twice at Hotel Pasquale on RS tours. The tour groups are usually divided so some stay at the other hotel the family owns, Villa Steno. It's higher up the hill than Pasquale but not too bad. I also stayed at another hotel on the RS 21 day Best of Europe tour at Albergo Punta Mesca which is nearer the train station in the "new" town and does not have a view of the sea.
There are trains from Florence that go to either La Spezia or Levanto which are at either end of the small train line that runs along the CT. You'll have to change to the local train at either of those stations. Monterosso is one stop from Levanto.
I do recommend that you have yourselves pickpocket-proof before you change to the train to CT. Have your passports, extra money, credit cards in a money belt under your clothing. Have money, phone, valuables in your purse in a zippered inside pocket inside a zippered purse with your hand on the zipper end. The pickpockets are looking for distracted travelers and getting off/on a train with luggage is a big distraction!