Turn 10 and diplomacy? That's not the Pyrrhus approach amigo.
Rome has more recruitment capacity than you do - they have holdings in two provinces, more regions in both, and your best troop recruitment area is across the water. Time is NOT on your side.
Here's what you do:
1) Recruit 3 pikes. Also, purchase 1 Mercenary Pike from the pool. You want max pikes possible, so at most you can recruit 3 and hire 1+1 next turn. That's 6 pikes in total and now you have a super solid main line.
2) Recruit slingers and Tarantine Levies - 2 of each at least. These are the cheap screen for your better units.
Optional) Depending on your funds, you may want to recruit some merc Cavalry - either lancers in Epirus, or Italian in Taras.
Addendum) Mercenary upkeep is now a LOT less than it used to be. You can now afford to purchase mercs whenever you want since they're less likely to break your bank. Consider them as an alternative to slowly recruiting cavalry and quality skirmishers, and as a necessary second source of pikes in Epirus.
3) By turn 3 or 4 (depending on weather and movement) you want Pyrrhus to have a large stack of troops outside Taras ready to go.
4a) If there is a Roman army nearby, pursue it and kill it. You want to be smacking Roman troops out of the air otherwise they will overwhelm you.
4b) If they're up fighting the Etruscans, march over and take Cosentia and occupy it. Don't Liberate. Those jerks always betray me.
5) If Rome is slow getting back, take......Campania/Naples/whatever to complete your control of Southern Italy. If you're worried about Rome and/or your army got too beat up, Liberate to create a buffer.
6) Here things start to branch. If you are doing well fighting armies, do your best to keep playing whack-a-mole. If you're having trouble, try and Liberate the two regions next to Rome to create a buffer zone.
It should be mentioned that Rome will get free armies once you start taking settlements. I believe Liberating counts, though maybe that's a Dresden and co question. Either way, that's why you want to cut down Roman armies when you can. Plus, with the new Vanilla update, you get money for all those prisoners you take in battle. Slapping Roman armies around can help keep your economy running.
Your strength as Epirus is that you have Elephants in Italy, solid pikes, and decent heavy cavalry once your Barracks lvl 2 is built. Thessalian Cav and the new Philoi Hippeis are more than a match for the Roman cavalry forces. You have decent melee infantry, but you lack the high quality Royal Peltasts that the other Diadochi get (Antigonids, Seleucids, Ptolemies). That makes taking Rome directly a.........frustration.
Keep a solid line of pikes, use your cav and light infantry to dominate the flanks and eliminate enemy skirmishers, then engage and use your elephants to rear charge.
Keeping Epirus safe on the mainland can be a bit of luck of the dice. Ideally, you get a treaty with Ardiaei, Makedon fights Athens forever, and everyone ignores you. At least until you've conquered enough of Italy.