Few start up questions

In my experience it depends on what your selling and who to.

My suggestion would be to have your standard terms being payment with order.

You could also offer the facility to pay via invoice with your customer opening an account with yourself.
The issue here really is more about the effect on your cashflow. This is then a far more complicated question.

I would set things up where business pay with order.

Most companies have a company credit card or can pay via bacs or some other direct payment into your account.

I personally know of 2 companies that went bust because they sold everything on invoice. Yes they where very successfull but it was actually their success that pushed them under.

Depends on your expected turnover.

If you turnover less than £15,000 your tax return is a very straight forward thing

Over you need to go into more detail.

Its wise to have a seperate business account to keep things simple for you and should the tax office question you other anything then its easy to clearly seperate things

Ltd Company vs sole trader I would speak to an accountant. There are a few on here that hopefully will give you a better analysis but I think youll have to give them a clearer understanding of your position.

More than one business simply have an account for each