Why the focus on the outlying cities? Our target is Rome and for that we have to go through Antium. Neapolis and Veii in particular can wait until after that.
The Preparation
First we need to deal with the troops in and around our territory. It is an advantage that they are there as they will be easier to pick off in the open than fortified in our cities.
Next deal with Hispalis and Ravenna that would otherwise leave Roman troops behind our lines. We will need to block access to the empty territory from the South from friendly nations who may decide to settle there until our cities can expand. This while gathering the remaining forces for the attack on Antium.
The main attack
This is the whole point of the exercise, without this we might as well forget it, so don't dilute our force by taking too many troops for secondary targets.
Next is Antium - take ALL the Trebuchet, with the accuracy they get they will be needed and with fortified Muskets we need every hit-point off we can get.
Our main target is Rome - throw pretty much everything at it, take it, reinforce it, starve it, don't let it riot (use the Governor if necessary) and rush culture as soon as possible.
Secondary Targets
The cities in the West need to go, yes, in particular Lugundum and then Lutetia (pity it was allowed to be settled so close), but these are secondary targets to the main attack on Rome an Antium. Once we have Antium and are moving on to Rome we should have a few more Knights and maybe even some more Trebuchet that will not reach the main force, or maybe even some spare from the main force (but I would rather not dilute that main attack force) that can gather and go for Lugundum and then Lutetia. We will need to leave a few troops in the western region to pick off any Roman troops that go that way, these can join in this attack as well.
Tertiary Targets
It would be nice if we could carry on and destroy Veii, Neapolis (or at least cut access to the Saltpetre) and the Roman city on the Silk to the North of Rome. But this will have to be if we have the resources to continue at this stage and are managing to cope with the war weariness that will probably be starting to set in by then.
City Investigations of some typical cities would certainly help planning the troops needed. At the moment we have no idea how many Muskets we will face: 6-8 in Rome? similar in Antium? 2-4 in Hispalis and Ravenna? maybe only a couple in Lugundum?