For day 1-3, for the train rides I would probably buy just regular one way tickets and a return trip.
You can purchase e-tickets online, those'll save you 1 euro per ticket compared to a ticket from a machine at a station. However, e-tickets are non-refundable.
Buying an OV-chipkaart is an option too. It's valid for basically all public transport. Valid for 5 years, costs 7,50 euro and you could save money on bus/tram trips you might need to make on days 1-3. Hard to tell. You could just make it easy for yourself and buy one, top it up and use it for bus/tram on days you won't be using public transport enough to buy a day ticket. Generally, using your OV-chipkaart is cheaper than a single ride on bus/tram. To use it on trains you need a minimum 16 euro balance to be able to check-in. It's not cheaper than an e-ticket for the train.
For day 2 it looks like you can use a U-OV day ticket for buses and trams in Utrecht for 6,50 euro. But I'm not very familiar with public transport in Utrecht.
Will you use public transport on day 3 in Amsterdam? Because if you do you could choose to buy a 3-day Amsterdam and Region Travel Ticket for days 3-5. You could also use an OV-chipkaart (for max. a few rides on day 3) and then a 2-day ARTT ticket for days 4 and 5.