An acid test kit only costs about $10. If you have an accurate pH meter (not test strips) you can test acidity by just buying sodium hydroxide and a plastic syringe, but a kit is probably simpler. Acidity in your peaches will probably be low. You can raise acidity with lemon or lime juice, but it does add flavor as well. I usually use acid from the homebrew store. You can buy malic, tartaric, or citric acid. You can also get acid blend, which is a blend of all three. Malic is the main acid in peaches. I'd probably use acid blend and malic would be my second choice.
Peach flavors tend to ferment out, so I like the idea of a port because fermentation is stopped before all the sugars and flavors are gone. I made a peach port last year and it came out very well. I prefer port to have a higher level of acid than wine. Port is normally sweeter than wine and it's good to have higher acidity in order to balance the additional sugars.