How long have you got?? Lol cut and dry you will pay huge tax on 2nd income as your allready full time employed, your time will become more valuable than ever, the words not enough hours in the day will ring in your head, i worked for a well known social housing firm full time whilst running my own door security team, each job allways clashed even though i started at 830am and finished at 2pm most week days i still didnt have time for my book keeping, hours , client liason insurance interviews etc it gets out of hand in the end, if you have a partner thats willing to help it becomes a team effort and is a lot easier on the both of you.
In the end i concentrated on the building side, now i work 80 plus hours pw and am away from my family for up to 4 weeks at a time go figure!!!! You get out what you put in my friend!!!!