uPVC windows - advice please four someone looking into buying them

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If replacing timber windows with uPVC what should I expect or look for?
For example the window sills inside and outside are timber. Will the outside be changed to uPVC and the inside sill be left timber? Will I need new wood anywhere internally around the frame/ opening?

Also please advise on window openings- "tilt and turn" etc. What's useful? And would you use toughened glass? It's a modern 2 storey house with a toddler living in it.

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