This diagram shows a city which has been built to produce Sesterces and other resources to supply my other cities: I have three such cities providing resources and Sesterces to the other two main cities.
It's a level 10 city not yet expanded to it's full size, but you'll notice that it only has 2 sets of barracks and 2 sets of workshops. Those are taken up in my main cities where troops are produced and I have 8 in each of those cities. Over 5 cities in total, I have 27 sets of barracks which are always making troops with the resources provided from my resource cities. On expansion I can include more barracks or anything I like.
Although the rectorate protects my Sesterces, and the 2 level 8 warehouses protect my resources, I don't need them because I transfer those into my main cities and into barracks and wall defences.
I do not keep troops in my resource cities because I want those troops in my main cities which defend my resources and Sesterces whilst I'm not playing.
If another player marauds the above city then he or she will gain nothing and will not gain any honor either because there are no troops to kill. I on the other hand have maximum defence in my main cities yet keep resources to a minimum because they are always being used to build troops.
Troops:
It doesn't matter what number troops you have for they will never be enough if you are attacked by an entire league or a greater number of players, each with more troops than you. Just build as many troops as you can and ensure you feature heavily on producing Onagers because they will provide maximum defence. You will know when you have produced enough of those when you are unable to keep up feeding, but use the food from your resource cities because there are no troops there to feed. You can set up an outpost too so that will transfer food automatically. I haven't gotten round to doing that with mine yet because I maximised spaces for cottages to produce Sesterces. When I expand the resource city I'll probably put one in then.
Running negative food:
Ideally, you should look to run into negative with food but make sure you're managing it right. The basic rule is if you are not in negative with your food then you haven't got enough troops. So as soon as you are able, maximise the rivers you take and always look to increase these levels until you have reach level 10 with 10 rivers. Then you're in business if you are still running negative with your food, but remember you are also able to maraud it from rivers and from other players, and of course you can buy it.Also note: You can simply reinforce your resource cities with heavy consuming troops like Ballistae and Onagers whilst you're playing, and recall them if you're attacked. This depletes the need to transfer food all day long and happily furnishes you with the ability to defend a producing city from invasion or give a scouting city reason to believe you lack proper defence units in your main city because they won't appear until you recall them to defend. You can also 'hide' troops in rivers and wildernesses and in other cities which you have colonised and simply recall them when needed. Remember though that they will still be consuming food from your city.
Defending:
Never leave your 'Engagement Protocol' as 'HEAD ON', unless you deliberately want to engage the enemy. Since you can see who it is who might be attacking you, then you have chance to consider if he has more troops than you before you engage. But remember, to look in your Arena if you are under attack because it might not be an attack but rather a maraud. - Remember that a maraud is not an attack and will not engage battle with your troops unless you have forgotten to untick 'HEAD ON'.
Secondly, if you are being marauded, then the enemy will not gain any resources from you if you have used those in your barracks and wall defences or sold them at market or moved them to another city, and your warehouses will in any event protect them if you have built warehouses to a good enough level.
Joining Arena:
When you see flames extruding from another city or from a wilderness, check in the arena to see who is attacking or marauding it. You might want to join them in the arena, in which case you will gain resources and you will have been assisted by other troops belonging to the other player. Note: It is best you do this only with your own league members unless you know the other player otherwise he or she might not like you getting their resources.
An expanded level 10 city with extra barracks and workshops and with 3 level 8 warehouses. (last one under production)
An expanded level 10 city with extra barracks and workshops and with 3 level 8 warehouses. (last one under production)
Notice my food is in negative 52,000 per hour. I want it into minus 200k per hour because that equals 4.8 million per day. I can supplement food from marauds, from production in my other cities and from knowing that all I have to do is to buy 5 million food per day, which you'll note is far cheaper than stone or lumber. Also, I am working to build up my rivers to level 10's so in essence they will allow me to keep more troops.

