The reliable way to hire a tradesperson

Having a patio layed using 450x450x50mm paving. A hot tub with approx 1.5 tonnes of water plus max 3 people to be placed on it. How deep should base be?

At the start of the project we were given a price of 5k and told no payment needed till after completion 3 days in, landscaper asks for 1.45k to cover materials and then to pay the rest in cash - I send it After the 3rd day he asks for another 1.45k to cover materials. I question as this is the second time he has changed his mind. Is this dodgy or normal practice?

I have 3 pots on my chimney. 1 fireplace in the lounge, 1 in the bedroom directly above and another fireplace in the spare bedroom. What would be supporting the spare bedroom fireplace having nothing directly below? Would this be built in the structure of the house? House is 1930’s 2 bed semi-detached