My suggestion is to seek out the advice of professionals in your area. Spend the time and money now to set everything up right, rather than spend more time and money later to make a change (if you make a "mistake"). Of course, there are many unscrupulous "professionals" out there, so beware.
No experience with sole proprietorship, but one thing I've noticed over the years. When LLCs and LLPs were introduced, I noticed a definite trend of existing companies to change to LLCs and LLPs (especially attoneys and accountants). I heard but can't verify, that it had something to do with income stream and double taxation.
An accountant recently told my mother that he generally recommends LLCs rather than corporations to his clients. But everyone's situation (and place of business) is different, which is why you should check with professionals within you local area.
Just some food for thought.