I'm playing the same campaing in RTR 4.1 and I'm loving it. Here's a brief description of it:

First of all, forget about caralis and the island north of that. The julii will attack you in few turns and land armies with princeps and hastati near your towns. I believe you can force them no to do that by destroying their army-carrying fleets, but I couldn't.

It may seems like a good idea trying to conquer Iberia, but Gauls and Iberians have large armies that will destroy yours soft militia and early hispanian infantry. Also your round shield cavalry should not be counted on when attacking good units, they flee after getting few losses.

Sicily may be hold but in my campaing scipii managed to bribe it and syracuse!!

So I decided to center on my homeland and trying to hold a piece of southern IBeria.
I searched for an alliance with egiptians, gauls and iberians but all we agree was with trade rights.

It is a shame because you are allied with them but you should center conquering numidia all the way to cirenaica. I decided to let them have Lybia because I can use them as a shield against egiptians.
It shouldn't be that hard to defeat Numidians and their cities are so far away from each other they will be hard to conquer by a foe.

Then I have to defeat invading scippis armies (really hard) wit the use of many mercs but I managed to get a good fleet and drive them out of chartage (be aware they will continue to attack by sea and that it is really better to sunk a navy with 3 units of triarri that having to defeat them in battle)

Scippis didn't have large armies in sicily so I could easily conquer those three cities. That's as far as I went (gauls and Iberians have allied and make me retreat to gades but it didn't bothered me that much).

About good units, there are three cities where you should build as many buildings as you can.
In chartage focus on infantry (3rd level let you build scuttari) and weapons , Thapsus should be your main source for cavalry (round shield cavalry are good if proper use, and your enemies don't specialize in cavalry) and Cirta should be your source for archers (2nd level of archery range).

Hope this can help. Build as many roads as you can and keep in good shape your navy.