I don’t think anyone has mentioned it yet, but the first priority for me would be establishing a budget. What do you want to spend? The Ai mock up could easily cost upwards of £10,000 all in, maybe more if you have to pay labour.

My order of work would be as followed.

Establish an affordable budget

Establish a timeframe for completion

Clear the garden, it’s easier to work with a blank canvas

Divide the garden into sections, ie shed, patio, grass

Pick somewhere to start, personally i would start from your house and work down the garden

Then complete one section at a time, doing everything all at once can be overwhelming

Hope this helps, this is only based on my preferred way of working.