This is actually a bit harder then something you can get a feel for by looking at a chart. You see level of the enemy is partially dependent upon the amount of battles they do. However the best way to find if you can beat an enemy, is to first scout and find their base, and then to watch to see which kinds of mines and salvage ships they are able to take out.
For example, I have Marauder ships, but by utilizing tactics I can take down level 5 salvage ships and level 7 mines (currently), at level 18 overall. So assuming I can take down level 7 mines and level 5 salvage ships, we can use this as a base line onto whether or not you will be able to take on the enemy, for an extended battle – meaning, you hit them, they hit you, and then back and forth till one of you stops.
The best way to see if you can take them on, would be to simply watch their fleets and determine whether or not you can take on the same level mines and salvage ships. If they often hit level 8 mines, and you have to send two or even three fleets to take on a level 8 mine, then this probably isn’t an enemy you want to challenge. The same holds true for the salvage ships. If you can barely survive a battle for a level 4 salvage ship, and your enemy takes on level 5s, then this probably isn’t an enemy you want to take on. If on the other hand, you take on higher level mines, and the enemy always goes towards lower level mines, then this is an indication of fleet strength.
However you should not confuse fleet strength with quantity of fleets. Some people like to show off their fleet “strength” by defending their base on the outside of their base. First off, this is both foolhardy and equally not well thought out. If I believe the enemy to be week – and offline – I will go ahead and take out the fleets first, then ravage the base. It might add some time onto my endeavor, but it won’t stop me from wiping you out and teaching you a lesson… repeatedly.
Tip: Remember, that the Fleet Master, which is shown might not represent the entire fleet. It could in fact be the highest ship within the fleet, with the rest of the ships being 1 or 2 tiers below it. Don’t be fooled with a show of strength, when someone defends on the outside.
If you don’t have the time to check the enemy constantly, then a good idea is to always take 2 from their base strength and use that to base on whether or not you can beat them. While I know I have some good tactics, the enemy might have better ones. By taking on a base 2 levels below me, I have a better chance of keeping him (or her) at bay.
Tip: Have a mine fleet and a base fleet. The mine fleet uses missiles and can take out enemy fleets, including Draconian fleets. The base fleet is more adept at taking out bases and missile defenses with mortar shots. A base fleet should have each ship holding at least 1 mortar gun.