I should add that those leaves are all new growth. In the fall, the plant looked severely sunburnt so I took off all the leaves.

Agree, those are normal looking plants. Yes, acid fertilizer, rain water if you can, don't let the pots dry out.

I'm worried because the last time I saw this (on the one that died), the berries ended up all shriveled and the stems also began to brown and shrivel/curl. I've seen pictures of various blueberry diseases where the flowers turn brown and the blueberry part and stem itself shrivels.

And I'm not seeing this at all on the "healthier" plant...To clarify, the second pictures are of the Sunshine Blue bush which is totally fine.

In the fall, the leaves had become reddish around the outer parts of each leaf and spread inward toward the center of the leaf. I later began to notice little green/black dots on the surface of the leaves (not w/in the leaf) that looked like spores. I then decided to pull off all the leaves and figured the plant was dying...But it came back.

What kind of soil did you use? I don't have much experience with bb as I started growing them myself recently but after tons of research, the correct soil mix, pH level, nitrogen, and I think iron is most common issues. I ordered plants from dimeo farm from new jersey and they told me to use a 50/50 of peat moss and coarse grade sand then fertile with Holly tone.

It's definitely fungal...Should've gotten rid of it. Most of the blossoms are browning and shriveling like this.

That last pic looks like Botrytis blight to me.