Building an army to Fight offensively is a bit different than building a good defensive army. Building an offensive army will definitely help your defense though.
First bit of advice is that it is good to have an assortment of offensive units. You can normally do ok without the long range units, but you want an assortment of the other 4. For the continent and GE, you get too see what you will be fighting, so choosing the right units is important.
Second, while perhaps not as important in EMA, soon you will be reaching the point where having a reasonable offensive boost gets very important. The first few percent don't do much, but by the time you get to +30% you will start to see a difference, particularly in the damage you take. In EMA you should have a Zeus that you are starting to level, which by itself won't do much until it has lots of levels, but the Cathedral of Aachen is just becoming available, and together they will give you enough to start to make a difference.
One side point, if you are looking for an army to primarily do the continent at a reasonably slow pace, and you do some GE, you may be able to pick up enough unattached units there to not need all 4 basic barracks, but us a few unattached units that you get as rewards.
One other big thing, more for GE than the continent, is to try to win a Rogue Hideout in an event. Rogues are possible one of the most valuable units in the game. The continent AI understands them, and fights against them better, but even there, adding a couple of rogues to your army can boost its power a lot.
