Completely incorrect - Companies, even limited companies pay NI twice, Employers NI (no limit) and Employee's NI (capped) for each employee. After the introduction of IR35 attempting to take all your salary in dividend will attract the full force of the Inland Revenue. IR 35 is a nasty piece of legislation, however there were pre-existing statutes under the 1988 finance act that allow the Inland Revenue (since the DWP were mereged with them) to make an assessment of earnings and levy an NI surcharge based on that assessment - it is then up to you to prove that the assessment is wrong. The 7 year limit for tax surcharges do not apply in these cases!
If you get the the point that you are making significant sales that could possibly be seen as income then the easiest route is to register as a sole trader. This allows you to offset expenditure, depreciation, maintainance, rent against sales income. You can also back date this against the previous years tax in the year you register.
If you get to this state you're going to need a good accountant anyway, and if they're any good they'll sort all this out for you.