Booking Train Travel and Private Transfers in advance?

In reverse order: You can do it on your own. No need for a travel agent, unless that would make you feel more comfortable. Private transfers would normally be booked in advance. I'm not personally familiar with any for Venice and since cars aren't allowed in the city, I'm not sure how that would work. You could hire a water taxi but I don't think the taxi would have to be reserved ahead. Hopefully someone a little more familiar with Venice can help you out here. With the trains, chances that first class, or even second class, are sold out are so low as to be almost non-existent. There's not much reason to buy your tickets before arriving in Italy, and with a U.S. credit card, it's very unlikely you would be able to purchase them without going through a middleman with higher prices. I typically just buy my tickets when I arrive in the city (if I know what time I want to leave). When we traveled from Rome to Orvieto, we bought the ticket the day we left Rome and it was an hour or less before the train left. You'll want to give yourself enough time to find your way around the train station, which depends on how big it is. The station at Orvieto is tiny and you would probably not need more than 10 minutes at most to buy your ticket and find your platform. Unless you are traveling on a very busy holiday, you should be fine, especially as most people travel in second class.

I think it is very safe to say that first class tickets NEVER sell out. Second class rarely sell out but it does happen on a few days. The only delay you could have would be the line for the ticket window since I assume you are not interesting in using the ticket machines. I generally buy my tickets the day before or if I know for certain when I want to leave, I will buy them when I arrive. I would ask the hotel to arrange the pick up in Venice. Just not familiar with private transfer since we never use them. There are always taxi available and you probably could negotiate a flat rate to Positano. But it is long way. With the internet it is easy to make your own arrangements but you need to trust yourself to do it.

Angela
I just booked first class ticket Venice/Florence on the Trenitalia web site last night. Even though the form said it would accept American Express it did not so I had to wait a half an hour to book again as it just throws you out of the system then I went back and payed with my Capital One Visa and got my tickets. There is a discount called the mini fare which is about a 20% discount from the regular fare. It seems there was only 2 available tickets in the mini fare whenI was booking for a May ticket as the system kept telling me there were no tickets in the mini fare 1st class for the half hour after my first 2 tries. From Marco Polo Airport in Venice you can take a Water Taxi for about 100 euro. I think it is about 1/4 mike walk from the airport exit to the water taxi stand. Some good info here: http://europeforvisitors.com/venice/articles/water-taxis.htm

The only reason to book ahead would be if you were certain of the trains you are going to take and if there's a discounted fair (e.g. MiniFare) offered for that trip. Be sure to read all of the terms and conditions for whichever fare type you decide to purchase. The Trenitalia website now accepts U.S. Visa and MasterCards, but only Italian AMEX cards. Therefore, once you create an account on the Trenitalia site you can purchase them yourself.

To get from Marco Polo into Venice, you can take the Alilaguna boat for 10-15 euro per person one way. Here's a link: http://www.alilaguna.it/index.en.html You might take note that July is a most popular month for Italians to take their vacations. My daughter found this out on her honeymoon two years ago. She and her husband were the only English-speaking visitors in their mountain resort.

Thank you every one for your replies! I really appreciate it and you've all allayed my fears about needing a travel agent. Normally I wouldn't even plan ahead so much, but since it's my honeymoon I wanted everything to be as "stress free" as possible. Seems like I needn't worry about train tickets and I will definitely either use public transport or contact the hotels we are staying at for private transfers. Thanks everyone!

Hi Angela We loved the transfer service at Laruscar@liberio.it. Eleonora Cavazza. Tell her David Loaiza recommneded you. She is really nice. We booked first class. I liked it because it seemed to be easily transferable if you miss the train (but check that).
I tried to buy on trenitalia website ahead of time but could not use my credit card. So I had a friend of a friend who lives in Italy buy it for me and I paid them. But it would be easier if you can make attempts(s) to buy ahead if there is a discount. Otherwise, just buy when you get there. As far as Venice we used the water taxi not the water Bus. It is more expensive but very convenient. If you need help I will but just search watertaxi services and check prices. If you need any other help just ask