Colin Rosenstiel wrote:
Do you have to buy a glass to use a seat?

There are a handful of public seats on the Midland Main Line concourse
and on the Thameslink platforms, but the rest of the seats are allocated
to cafes, restaurants and the champagne bar (which has plenty of seats,
hence my earlier remark).

Not so much legendary as long departed. You mean Midland Curve surely?
Hotel Curve was from the Widened Lines up to the King's Cross suburban
platform 16, long since gone.

If the Midland Curve is the section of King's Cross Tunnel where the
carriage length limit is significantly restricted due to the severity of
the curve then yes.

How will one get a bike between the platforms and street level then?

If the lifts (let's call them 1 and 2) are big enough then your options a
Street level - Lift 1 - Southbound platform
Street level - Lift 1 - Mezzanine - Lift 2 - Northbound platform