Depends on exactly what your definition of battery is. You state "12 1350a/h batteries". Is each battery a single 2 volt cell? If it is, then you have a 24 volt 1350 AH Battery. 12 * 2 volt cells (in series) makes 24 volts. The total capacity is commonly known as "C". Maximum charge and discharge rates are commonly expressed in fractions of "C". C/10 and C/20 are commonly quoted as discharge rates for specifying actual battery capacity. These same ratios are not unreasonable to be used for charging ratios as well.
For instance, a 1350 AH battery pack would take 10 hours to charge at the C/10 rate, and 20 hours at the C/20 rate. The C/10 rate in this case would imply 135 amps, and C/20 62.5 amps. It would take 135 hours to charge said battery pack from dead flat at 10 hours. That's 5 1/2 days at 10 amps. (yes this is simplified and ignores conversion losses in the batteries).
So, in answer to question 1. 62.5 amps would not be unreasonable.
My dump load controller is set to start dumping at 27 volts normally, and 28 volts when in boost or equalisation mode.
Eq at 28.8 is not unreasonable. Bulk charge should be a lot less than 31. 27 point something sounds good to me.
Generator run time needs a whole lot more inputs related to battery state of charge, current load, future short term load, current and short term future generating capacity outside of the generator. In short, a really big crystal ball.
hope that helps.
Amanda