This is my "day job" domain.
This all looks fine, but Cat 6 cannot simply be "slung in" by electricians. There are issues with bend radius and termination procedures. There is no point in paying a premium for Cat 6 if it isn't installed and terminated properly.
Capacity. Yes, make sure you have space in your rack for a bigger switch. Customers seem to need 50% more than their day one planned requirement. And, likewise, cable. Always be generous with cabled points versus capacity. And make sure that cable routes have decent capacity and are accessible.
And, of course, if your ADSL is poor, much of this won't work well. And what happens if your ADSL goes down?