Do I get a gas cylinder with my purchase?

No. You will need to purchase a gas cylinder yourself. The built-in burner only works on propane gas. For example, you can use this 3,9kg propane gas bottle by Calor: https://www.calor.co.uk/shop/gas-bottles/propane-gas-bottles/3-9kg-propane-gas-bottle.html

With a 3,9kg gas cylinder like this your fire will last for about 10 hours.

How large are the built-in burners?

The built-in burners have the following dimensions:

60 x 30 cm (model Twist)

42 x 42 cm (model Cube & Leaf)

What is the size of the safety glass?

The size of the safety glass of the 42 x 42 burner is 50 x 50 cm. The height is 17 cm. The size of the glass of the 60 x 30 cm is 65 x 35 cm. The height is also 17 cm.