You can post here if you like as there are no separate subforums for submods!
I haven't played the Romans in GC yet myself so I cannot comment on how to proceed with them. I did play with them in CiG though for a bit and it was fairly enjoyable! One of my friends who played them in GC said that it was a tough nut to crack Pyrrhus first but once that was done and the Etruscans were gone he could continue up north into the Po valley. Apparently keeping half an army at the southern town is enough to keep Syracuse at bay.
Early game I always use cheap troops (no matter what faction I play) with only a few good units, since the AI mostly does the same. Due to the Romans having some of the most expensive troops I'd probably want to mostly use levy-class units early. As for taking Taras from the Greeks, you could use a "trick". Siege it with a small force (4-5 cheap units) and have your real force standing beside it. Make sure there's a supply route into the region too - that way you can wait them out without taking attrition with your main force from besieging (and no famine in case supplies end)
The PO negative was nerfed from -35 to -25 a few patches ago!
Dignitary agents are very important in DV (I've increased the amount you can have, but they also cost a bit more than in vanilla DeI) for maintaining your kingdom in all its aspects. Economy, public order, culture, empire maintenance, building -% construction costs and research bonuses all come in handy from their selection of skills. I suggest the first thing you do is to tech so you can hire more dignitaries. Also keep at least one general in each province as a "city governor". Only level governor skills with these characters, it will boost your public order/income by quite a lot as they become better and better at governing.