How fast and how big different classes of ships should generally be?
The "correct" answer, which I am sure that many people are furiously typing right now to be the first to tell you, is "whatever you want", which is true but not very helpful for newer players trying to situate themselves in the game.
As such, I offer the following general guidelines:
- Escort classes: 5,000-10,000 tons: these could be point defense escorts or smaller ships for patrol and security roles.
- Midsize classes: 12,000-18,000 tons: these could be larger PD escorts or midsize, workhorse combat ships like cruisers.
- Large classes: 20,000-30,000 tons: these could be capital ships or large cruisers at the core of a large battle fleet.
- Typical large battle fleets should probably be in the range of 150,000 to 300,000 tons. Smaller fleets for, e.g., patrol or colony defense can be anywhere from 1-2 small ships to perhaps 30,000 to 60,000 tons.
These values will put you roughly in the ballpark of the NPRs you will typically face. Note that you are by no means required to have ships of every size class, for example an early-game fleet may not have large capital ships yet and this is fine.
For reasonable fleet speeds, a good rule of thumb is 30-40% of total ship mass with a base engine power modifier (1.0x), which again will keep you competitive with most NPRs. Once you are comfortable with the game you can deviate from this rule in all sorts of ways, although I don't recommend playing around with the EP modifiers too much until you are comfortable as this is a good way to drain your fuel very quickly if you're not careful.
Additionally, I recommend that ground formations be in the range of 15,000 to 20,000 tons each, in general. This is a good rule of thumb to make sure you are getting the most out of your ground force commanders while building up the multiple millions of tons you will need to assault an alien home world.