I just recently ventured out from spinning wool to alpaca and I have an Ashford Traditional wheel as well. Big difference! I found that compared to wool, you need to slow down your treadling and let it twist more. I also found that I need to draft more slowly as well to get the thinner yarn. Every time I start spinning I have to repeat "SLOW DOWN!" in my head until I get the right pace.
I use the Joy of Handspinning
website for reference when I need more information. I also ask the spinners on the Knitter's Review Forums
for help as well.
I can't help much with the price of selling roving but you could research eBay
for what other people are selling it for.
Good luck and post lots of pictures!