Not counting the limes, how sour do 3x-4x peels stay? I'm assuming that navel & blood orange peels won't have that problem. Also with oranges, are hand peeled peels still viable for candying or do they lose too much pith? Could straight frozen peels work (fully thawed)?
It depends on how often you blanch them and for how long :)
If you want them to stay bitter I’d only blanch twice, but you could totally test them as you go along in between blanching them to see how bitter they are and use your own judgement after that. If I want something fairly sharp I will only blanch twice before the syrup immersion stage. If I want it more candylike and sweet, I will blanch them a few extra times and test them when I dunk them in cold water in between boils.
By hand peel I assume you mean when you are peeling them to eat, I mean, I guess that could work? I’ve never actually tried it that way because there’s never enough pith left to make strips. You could however chop all that up really fine and sprinkle it in to cake mixes if you wanted to.
And yes, you can freeze peels and have them work just fine. Cooks and bakers who use a lot of lemon juice but don’t necessarily need the skin right away will often zest it and put it in a freezer safe container to take out whenever they want to add to cakes or other baked goods. Just make sure it’s washed and allowed to air dry thoroughly before you freeze it, otherwise it might be watery and mushy. You can also freeze whole lemons, but the insides will only be good for juicing after thawed cause it goes splat. The skin should be fine though. I personally like to freeze lemon wedges to throw into drinks. Which also makes them easier for getting peel for candying too and then I dont have to deal with scooping out the mushy insides if I want to make peel.