I didn't experience any reboots when not signed into google after a factory reset so I signed in and restored my tablet using Google backup.
I soon started to get reboots again, but I noticed that since the KitKat upgrade a website I use very often was sometimes automatically loading the Play store to try and get me to use their much inferier app. It doesn't happen on my Note 3 which is still on 4.3.
If I tried to close the Play store app to get back to the browser by swiping it away then it crashes and keeps trying to load over and over. If I hit the home button the Play store automatically re-appears still loading over and over, but after swiping it away several times it goes away or stops with an error message asking me to report the crash which I did and the browser is closed.
In order to fix this I disabled the Play store app so that it did not appear in my list of apps.and the website instead of loading the Play store app re-directed the browser to the Play store website which was better for I was still in the browser.
Since I stopped this particular website loading the Play store by removing it, I've just had one re-boot instead of several and my tablet is no longer overheating. I am a heavy user and have my tablet on many hours a day, so one re-boot is acceptable to me.
I've downloaded a Play store apk which I can install if needed but always remove it before using the website which tries to automatically load it.
It is a nuisance and I wish I'd stayed with 4.3, but I can live with the occaisional re-boot that might not be noticed if I only used my tablet lightly.
I'm annoyed that a website can automatically load the Playstore without me requesting it and that KitKat allows it.
I hope my experience helps others who are getting several re-boots a day.
I did a factory reset then removed the Play store app before using the problem website so that it never loaded it in case that was needed.