Heated bed with a PT100 sensor and a LERDGE "K" control board would be a good start. LERDGE supports TP100 as a standard plug and play including auto calibrating the PT100.
I use a mirror glass of 3 mm (with real metal coating) on an aluminum bed 310x310x4, with no need for auto leveling. The build is within 0.05mm flat and leveled and stays that way.
A large bed of 1000x1000 mm would ask for quite some thickness. To keep such a plate flat please think about quality type AW 5083 (or similar for North America), it comes milled or grinded with flatness <0.05mm. Just regular warm/cold rolled aluminum will keep on deforming a LOT when heated up and cooled down again. (will not work)
I have designed heated bed plates of 1200mm in diameter, with sandwiched in between two long hot runners imbedded with copper paste for contact purposes. (my application 120 dgr Celsius) The AW 5083 material stays flat under all conditions if well isolated and enclosed. (For even cooling down and heating up)
If you like to go cheap on this huge heated bed design, and think all flatness problems will be solved with auto-leveling, ….. a disaster is guaranteed.
The XYZ movements/mechanic design is simple and quite standard. (THK linear guides (or similar quality) with "Caged balls" are recommended)
I added a 1200 mm sandwiched hotplate design from 2011 I believe it was.