If you cease as a sole-trader during the current tax year, you will need to draw up your final accounts from the start date of the current accounting period which would appear to be 6 April 2015 to the date of cessation. Those accounts should include all your business income and expenses to the date of cessation.
If you have a balance in your sole trader account, some or all of which you wish to transfer to the new limited company account, then you can do that and it won't be taxed as income of the company because it will have been accounted for and taxed through the sole trader business final accounts which you will disclose to HMRC in your 2015/16 tax return. As far as the company is concerned, the cash injection will be treated as capital introduced or as a loan to the company which you can withdraw with no tax implications as and when you see fit.
Once you have completed your final sole trader accounts, you will know what the taxable profit is for the final accounting period which will all be taxable in 2015/16. That will tell you if you can draw income from the company up to 5 April 2016 and pay no tax. Dividends would allow you to do that because, until 6 April 2016, they will be treated as basic rate tax paid.and provided your total income is no more than £42,385, you will have no personal tax liability on the dividends.
Take a look here
for information on incorporation relief.
I hope this helps but let me know if you have any further questions.