2 Questions: Frozen peaches? Ripe or "almost" ripe best?

For best results, use peaches when they're perfectly ripe - not too underripe or overripe. When making a tart, it's a good idea to partially thaw the slices beforehand, so they can finish thawing and cook properly. I follow Nancy's method of freezing peach slices and storing them in 1-pound vacuum-sealed bags. I haven't tested if they last a full year because I never have enough frozen peaches. For other recipes like pies, thaw the peaches and drain them to save the juices. You can use some of the juices in the pie and the rest in drinks like tea. For cakes, substitute peach juices for some of the liquid in the recipe or brush it over the finished cake https://www.junkrecolet.com/

It's also best to use peaches at their ripest- not slightly under, and not so much over-ripe either. When you want to make your tart, you would do best to partially thaw the slices before assembling it, so the peaches will finish thawing and cook in the given time range. I also use the method Nancy gives to freeze peach slices, then package the frozen slices in 1 pound vacuum sealed bags. I don't know if they would last a full year, because I have never had enough peaches frozen to discover that. For other uses, like in pies, I find it's best to thaw the peaches and drain them in a sieve over a bowl to rescue the juices. Some of the juices can go back into the pie, and the rest goes into a pitcher of tea. If you make them into a cake, use the peach juices instead of all the liquid the recipe calls for. Or brush it over the finished cake after baking.

Ingredient list favours ripe peaches.
To freeze them - slice, Soak 5 minutes in dilute lemon juice, freeze 4 hours on sheet pan, put in plastic bag. Keeps 1 year.