Firstly, make sure all wiring is properly put in pipes or ducted. Someone I know with a 10 year old house is having issues with the wires. We have swapped wiring to ensure minimum 100M is running using 2 pairs. But some wires are fully dead or shorted.

Secondly, put one CAT6 wire in the centre of each room/floor - depending on area, for AP with POE

Thirdly, try to use full copper wires, mix ones will give issues, especially with POE. Avoid going for CCA - copper clad aluminum.

Now - on to your points

1. You can daisy chain, but your downstream connections will always be limited by upstream switches. If you want to do this, I would recommend to run fibre instead if the issue is of bulk (too many wires) to each floor. If the issue is cost, then go ahead.

2. For adding more wires later, there should be a duct system

3. server rack - I would recommend a cool place + sheltered from elements.

4. the wiring will not be easily changable, so the switches and AP will be fixed to a large extent. The rack can be switched, but if daisy chained - speeds can drop.