I'm in accord with "sharp shooter" ... particularly in regard to quality reloads and
buying in bulk. For me it still makes sense to do so ... using a P/W 950 Elite
and running through between 5,000 and 7,500 rounds a year.
I've purchased (cash & carry) lead by the ton, and
primers and wads by the sleeve/case of 5000, respectively. In addition, I've
been using Alliant "Promo" for the past several years, at about $100/8lbs.
I've found it to be very comparable to Red Dot, albeit slightly "dirtier" ... which is of
no import to me ... or my O/U ... and neither of the autoloaders have been problematic either !
At any rate, it all disappears with good cleaning practices.
With something in the neighbourhood of 50,000 old style once fired AA's and
15,000 or so Federal GM's on hand, I won't be buying any empties anytime soon.
I enjoy shooting factory stuff ... STS's and Federal papers in particular, but good old
AA's, Kent, Gamebore, B&P, Fiocchi and a few others offer some very good loads as well.
In the end run, reloading to achieve a quality reload is still less expensive for me
than buying first class target ammo, and far preferable to using "promo" ammo.
As to your original question: "Where to Start ? "
I think one of the best sources is probably Lyman's "Shotshell Reloading Handbook"
Tons of info on the basics, components, "how to reload", shotshell ballistics,
information on chokes, reloading for special purposes, and extensive data for
loading all gauges for lead, plus popular buckshot, slug and steel shotshell loads.
Haven't seen anything on the internet that even comes close.