No practical experience here, just lots of reading, so somebody correct me if I'm wrong, but as far as material goes, stock will be fine. You only need to worry about more exotic pushrods for strength/weight for crazy high spring pressures, solid lifters, and/or more rpms than these tanks can ever hope to achieve. Length is another issue though, and will be determined by rocker arm geometry. Stock rockers will be fine, but some aftermarket sets require longer rods.
Probably not, unless your cam has aggressive lobe ramps and you're running more than 280# or so of spring pressure open. I'd be more concerned with the stock T's on the rockers if those are still in use.
I ran a 472 hard at 5000 rpm often using a Comp 268H cam and sbc replacement springs and retainers. Stock pushrods did fine.
Beyond that point I'd upgrade. Cad pushrods are long!