Hi Hofkissed,
The power of Twitter is in numbers. You can scale your account relatively fast if you keep following members that twit about things relevant to your niche. If you have less than 1000 followers on Twitter, you are almost invisible there and can't get enough traffic to secure sales. So the more people follow you, the better. It will also get easier for you to get followers, once you hit a 1000 mark. People like following popular accounts.
How many times per day should you should twit?
There are many different opinions and studies out there - when to twit and how much. You can Google this topic and share with the group what you found useful.
I'd say it's a trail and error situation. Try certain number of twits per day and see if the number of your followers grows or drops off. If they are consistently dropping off then slow down a bit. I think if you twit or re-twit interesting things (sale items & new products fall into this category too) than people will be happy to see your posts. Keep in mind, nobody sits on Twitter all day, so if you twited 20 - 30 times a day, some people will notice only 1 or 2 twits. For that reason you can repeat some twits to make sure more people saw your important messages.
When Guy Kawasaki was talking about his use of Twitter, he said that he tweeted every story he wrote 4 times. The exact same tweet. His rationale was that his audience was tuning into Twitter at several different times during the day and he found that 4 was the optimal number to convert enough of the people reading his posts into traffic back to his website.
So start experimenting with the number of twits you post every day and let us know what you are noticing.