I'm a dog walker :) I started about a month before the pandemic hit, which wasn't the best timing on my part lol. I'll try and answer some of your questions though!
How did you start?
It was basically a random idea, lol. My old job was destroying my mental health and I was job-hunting online and found a job in the local kennels. I didn't get it, but it inspired me to look into working with animals and it kind of went from there.
What is the first step I should take?
Get yourself qualified in canine first aid (there are plenty of courses available online and in person) and ideally take some classes in canine body language and behaviour. The IMDT are the best place to go for training courses but they're not cheap. Being properly qualified is essential if you want to go down the training route, though.
For walkers, there's no requirement to have any qualifications but insurance is an absolute MUST. I'm with Protectivity, but Clivertons and PBI are other good options you could look at. I pay less than £7 per month and it covers me for walking, sitting, pet taxi and even grooming etc. if I was qualified.
Would you recommend volunteering/shadowing an already established Walker?
It depends, as not all dog walkers work the same way. I wouldn't be afraid to ask, though. It'll get you used to the timings, routine and walking in all weathers too. You'll need to invest in decent waterproofs (jacket and trousers), good quality socks and comfortable, waterproof shoes.
I was wondering how holiday leave would work because obviously I want to be consistent.
I give my clients as much notice as possible (ideally 6-8 weeks) and then just take it. You do lose income but that's part of being self-employed, really. It's not viable to never take a break. I would also say don't fall into the trap of working seven days a week!
Also, it sounds negative, but think about the following:
Can you comfortably take multiple dogs out together safely? Solo walking is hard on the body and it's much harder to make good money that way.
Do you have a vehicle that's safely kitted out with tethers, seatbelts or crates? Make sure you get business insurance too.
Would you know what to do if a fight broke out amongst the dogs?
What about if one of your dogs got injured or slipped their lead and ran?
Are you happy taking care of all breeds and ages or would you be happier specialising in, say, gun dogs or hounds or small dogs?
Could you cope with a reactive dog, or a dog that lunged or pulled on the lead?
Good luck. You could try joining some of the dog walking groups on Facebook for more advice :)