That's your typical question-with-a-thousand-answers for APUG because everyone uses something different and thinks they have The One True Way. However, my guess is that you should sell:
Originally Posted by vcyoo
- D76 (most basic and cheapest do-everything developer, been around forever and very hard to beat)
- Rodinal (huge unfulfilled demand for that in AU right now, see the various whinge threads on APUG; Vanbar have been backordered for months)
- maybe HC-110 or LC-29 (both are liquid and easy for beginners, you only need to stock one of them as they're so similar)
- maybe XTOL
- Rapid Fixer; brand is irrelevant as long as it's ammonium thiosulphate
In terms of tools, I would suggest that you be minimal and carry only:
- Paterson System 4 tanks, probably just the 2x135/1x120 tank with spirals,
- dark bags
Nothing else is worth competing for because people can buy a $2 thermometer off eBay and a $2 measuring jug from KMart, etc.
If I were you and planning on stocking ANY equipment, I suggest an "all in one stuff you need to do film development" kit aimed at lofi (if that's really your market and not us APUG nerds) people looking to move into their own B&W. It'd need a tank+spirals, dark bag, thermometer, 500mL plastic kitchen jug, D76 or LC-29 (plus a 10mL syringe if supplying LC-29, make sure it's one that fits through the neck of the LC-29 bottle), rapid fixer and photoflo. And some good, simple written instructions - you'd be surprised how incompetent people are at looking this stuff up.
Of course, people can buy dev equipment off eBay too, so I wouldn't bother stocking any equipment for development at all, just some consumables. Likewise I wouldn't go into selling darkroom/printing stuff like paper either; in my imagination at least, people who do wet printing make big overseas orders every 6-12mo and only buy local if they need something TODAY, in which case your store will miss out anyway since it has no shopfront. Paper is also really heavy+bulky.