Nay

On days you are in port, you can probably find some free wifi somewhere.  Some port towns offer municipal free wifi.  A lot of restaurants on the islands also provide it to customers so pop in for a drink and call home.  (Be sure to setup/enable wifi calling before leaving home.)
My parents needed to reach me while I was on a cruise last year so they called Royal's main customer service number, provided our ship and room number, and were put through to Guest Services on board.  We weren't in our room at the time so Guest Services left a message saying my parents had called and to stop by their counter to receive a complimentary call home.

Wifi-calling and texting are features of your cellular provider and smartphone.  For example with TMobile on my iPhone having activated wifi-calling at home on my home wifi it works on the ship over Voom.  It's important to use it at least once at home prior to sailing.  For help with that go to a store for your cellular provider and ask them to help you activate it.  
As far as purchasing Voom it doesn't matter if you book it using the cruise planner or through your agent.  While I book my cruises using a travel agent, I make my own cruise planner purchases.  

ChristineS, We are going on the same cruise but in Feb '19 We have never cruised and I really wish it was sooner, cant wait...hard to wait. Hope you enjoy!!

Typically, your hotel will hold your luggage prior to check-in or post check-out while you are out sight seeing.  When we stayed in San Juan our hotel even had a room by the front desk to hold luggage.  They tagged our luggage and gave us claim checks.  It appears to be a common occurrence.

I agree with @Clear Laker . The hotel will gladly store your luggage.