Re: Yeast; starters and oak
1. The yeast will be fine as long as its not 80-90F (and I know it ain't up there where you are).
2. I assume the additional wort has been boiled to sterilize, so yes.....however there will be a point to where the yeast cell population consumes all the nutrients during oxygenation and begins to utilize the glycogen stored up within the cells - which will be needed for the best performance of fermentation (no off flavors, attenuation, excess esters, etc.). This can happen rather quickly, otherwise you'll have to prep starters every day for continuous feeding and continuous brewing (well, worse things could happen).
Also, the second runnings may be low in amino acids - and thats bad for propagation. Do we need to open Camp Al B for microbial kinetic programming? ;)
Yeast get tired during fermentation/respiration due to depletion of glycogen reserves (population of pitch and health dependent), alcohol to a lesser degree.
I like yer stamina in these 2nd running projects, I never bothered after drinkin a small beer once...........once.