At LtCommander it shouldn't affect you hardly at all. The differences between the ships and abilities at that level are far less than at higher levels. You'll but able to use 2 engineers rather than 2 tactical officers that you would in an escort. So have fun with you Excalibur and don't worry too much about it until you become a little more familiar with the game.

You get the first ship free at Lt Commander but can buy a second one for approx 20,000 energy. So if you want to see the difference between Cruisers and Escorts it's not that difficult to save up for an escort after you get your Excalibur. Escorts are a lot more maneuverable but a lot weaker than cruisers, and escorts have 3 fore/1 aft weapon slot where cruisers have 2 fore/2 aft. It'll be more about which play style do you like more.

You might find the Skills: The Numbers link in my sig to be useful, although depending on how familiar you are the the game, it might be an idea to start with the Character Basics link instead.

Hope one or both are helpful.