I dont own a tube amp. This is just out of my personal wondering. I am not buying one either nor do i have the overdrive pedals. I am a broke bastard more or less. Its just something i've wondered alot. Distortion pedals are supposed to usually emulate tube distortion or a very heavy metal distortion or whatever.

Now when u have a tube amp and u want tube gain without the distortion what would happen if you ran multiple overdrives like had 2 or 3 or even more overdrive pedals one after the other with them all on, full gain and all tht crap then had a noise suppressor like a Decimator to get rid of the noise. What would it do? would it push your tube amp really hard and make it a beast for metal or just not do much?

Another thing is I know distortion comes from cranking the volume and making the tubes hot. What would happen if a person left a tube amp on for a long time like an hour then came back. Would the distortion be heavier or the same?

Once again I dont have money for one, its just a stupid wonder i've been having.
overdrive doesn't push tubes harder. it clips the signal. running two or three would just have more gain.

no, leaving it on to heat up wont make it brutal-er. it shouldn't heat up past a certain point anyway
Some people use overdrives with gain almost at 9 o clock and almost on full volume, this works great both on clean channel to add some dirt and also on the distortion channel to make it heavier. This is something in between an overdrive and a booster.

Cascading overdrives won't help you if you're lloking for a metal tone: AFAIK SRV had two tubescreamers cascaded for solos (ts808+ts9?)