I can't help you with your second question. I would guess that it would be okay, but definetly don't hold me to it

I can offer stocking advice though. In a 30 gallon tank you want to have about 30 (maybe 35 if you really stay on top of the water changes) inches of adult fish. Your tank would be overstocked with the above stocking list. I'll show you how many inches you are currently working with and then give you an idea on how to modify it so that it works
Current List:
4 Black Skirt Tetra (2.5 inches each)= 10 inches
4 Serpae Tetras (2 inches each)= 8 inches
2 Siamese Algae Eaters (6 inches each)= 12 inches
2 Fancy Guppies (1.5 inches each)= 3 inches
7 Cardinal Tetras (1.5 inches each)= 10.5 inches
1 BN Pleco= 4 inches
The cherry shrimp won't hurt the bioload of your tank much, so I would probably go with 5 of them and no more than that.
Total Inches: 47.5 inches
Working with the fish that you already have in your tank, here's what I would do:
4 Black Skirts: 10 Inches
2 siamese algae eaters: 12 Inches
1 guppy: 1.5 Inch
4 Cardinal Tetras: 6 Inches
1 BN Pleco: 4 Inches
Total: 33.5 Inches
You could probably add in a few cherry shrimp and you would be all set.
I hope that I was helpful to you

Just for the record, I have had a really good experience with black skirt tetras and have come to really like them. I also love bn plecos. I just got a LFBN about a month ago and he is so cool! Good luck with your tank! Post some pics when you get a chance.