LTD company is a big investment in terms of time and effort, and unless you are planning to quite your job in the near future and work on this full time could cause you a world of pain.
Bottom line is you want to be a Soul trader (spelt correctly this time) and make sure you are aware of what tax rules apply to what job.
eg: tax for 9/5 job
tax for free lancing
how each effects each other.
And I know I've said this before, but please please check your current employment contract for your 9/5 job for things like
You must not engage in business dealings outside the company within the same industry
You must not hold shares in rival companies
eg: make sure there is nothing your current contract that stops you doing this, as I say, I know of two people who have lost their jobs over it. Its not normally an issue if you have this setup before you start a job, but as your making a decision to do this while employed with your current employer you could end up in a real mess. It /may/ even be worth sounding this out with your boss/HR person at your current job, and if you don't think that would be a wise move as they may not be happy - think how unhappy they would be if/when they find out your doing it behind their back