First, you need to break in a briar differently. It will taste like... well, briar for a while. that may be the acrid taste you're noticing. Put fifteen or twenty bowls through it and you won't notice a thing.
My briars almost always have a bit of moisture in the heel. That's normal. Dottle is normal. You'll have a perfect moment where you'll smoke it all the way to the bottom without excess moisture or relights but that isn't normal. Don't worry about that.
The inside is cake. Cobs are much harder to grow cake in than briars. The bumpiness is carbon build up and that's good. That'll cover up the inside of the briar bowl which will minimize the sour taste you're noticing.
I think it's also important that you smoke mainly inocuous tobaccos through it at first. Prince Albert, Carter Hall, etc. Break it in before you start smoking any really sweet or really savory tobaccos. There is a much larger margin of error with a new pipe when it comes to both sides of that spectrum.