Well guys, it's finally done, finished, finito! Plumber showed up a few minutes after noon and left at around one.
He said it was a shame, because I was so close, but it wasn't anything I did (I asked him if it was my fault it was leaking under the sink).
He replaced the water lines, had to adjust the valve seat or whatever that brass thing is that the cartridge goes into. Evidently when I was having my husband tighten it, it raised it up. It also did all kinds of other adjustments (at that point, I didn't want to seem like I was breathing down his neck, but I did ask him lots of questions).
Then he caulked around the sink, and that was that.
A big part, or maybe the whole reason, for the low water pressure was the horribly clogged up aerator. My husband had tried to get it off, but didn't want to totally ruin in. So the plumber was able to get it off, and cleaned out the aerator and pressure was normal again.
Lesson learned I guess. Next time get a new faucet and hire a plumber to install it
Oh, by the way, did I tell you I have a drip from my kitchen faucet.......
I want to thank all of you for all the help, insight and support throughout this fun project.