Should I request a zero hour contract for my second job?

So I'm currently employed full-time at my new job. But my old company has asked if I would still be available for some freelance work on the side. The work would come about twice or maybe three times in the month and at average each job would take around 5 hours. And that's not always a guarantee. There may be some months where there's no work. But it's good to be able to make a few extra pounds on the side. So I was wondering if it was worth asking my old employers if I could be put on a zero hours contract. I don't want to get into the mess of doing all the tax work and I would rather it was sent to me as a PAYE payment rather than me having to sort out all of that before all the deadlines. I'm of course very new to this so wondered if I was even allowed to do this legally and if so am I making the right choice? Also would I need to do anything further or would my old employers take care of that once they put me on that contract? I understand that these are all probably very naive/silly questions so please go easy on me in your replies. Thakns!

Hi Haximus,
You can have 2 jobs at the same time.
If the freelance work with your old employer will be as an employee the employer will send the starting details to HMRC and we will issue a tax code to enable the correct tax to be paid.
If the freelance work will be as self employed and the gross income will be £1000 or more then you will need to register as self employed and complete a Self Assessment tax return
Set up as self-employed (a 'sole trader'): step by step
Thank you.