Hi, it's been years since I've fitted a fire door and I've a job coming up where I need to replace a door leading from a kitchen to an office so I wanted to run a few question past you folks. The frame will be staying in place so rather than try and fit a fire and smoke seal to the frame, can say a 15mm fire and smoke seal be fitted to both sides and head of the fire door? Also I can't remember intumescent hinge pads being a thing years ago so are they a requirement both on door and frame when a new door is fitted? 

One last query is due to the door being thicker and the stop needing moved over, are there any requirement s regarding door stops that I should be aware of?

The main consideration is that many 'standard' fire doors have a strict limit (usually 3mm/4mm max) for trimming the edges to suit an existing door frame. So check the sizes before you buy.

Combined intumescent fire and smoke seals can be fitted in the edges of the door leaf or in the frame. Make sure you comply fully with the door leaf manufacturers installation instructions including the self-closing device and sealing the gap between the door frame and the surrounding wall.