I made a tactical officer for my first captain and while I am still leveling I don't think I've used any of my tactical only abilities for space combat yet. Are career abilities important later on or can you choose any class with any ship and perform all the roles just fine?
As you progress you will gain more abilities that are specific to your chosen carreer. So as a Tactical officer, you'll only gain Tactical abilities. You can however fly any type of ship. You're not restricted to Escorts, but you can pick a Cruiser or Science Vessel if you want. These will give you more Engineering and Science bridge officer stations, which allows you to use more of those abiilities.
If you find that you can beat space combat easily without having to use any special abilities, you may want to consider increasing the difficulty level. This makes things harder to beat (obviously), but also increases the amount of skill points and loot you get from things you defeat.