Hi lozza, you probably won't find this very helpful but the answer is something along the lines of 'how long is a piece of string' I'm afraid.
Our firm specialises in assisting new business start ups and an increasing number of these are web based businesses. The experiences of these businesses varies hugely depending on all sorts of factors - your product, the demand for your product, your pricing and marketing strategies etc etc.
It might be an idea to prepare a business plan and financial projections (if you don't already have this). Some people see this exercise as a bit of extra work that they would rather do without, but the advantages in doing this are that it helps keep your mind focused on what you need to be doing, what you want to achieve for your business and how you plan to acheive it. It can sometimes help to sit back and try and look at your business from a distance to ensure you are staying on track.
Acheiving a good turnover is obviously very important, but you also need to be just as aware of what your gross profit margins and overheads are to ensure that the turnover is actually translating into profits and income for you. You may well already be very aware of these - it's just that as you have only mentionned turnover in your thread, I thought it was worth mentionning.
Best of luck with it all and feel free to PM me if you are looking for any help.