I would say the same - go to lots of shows,join local hamster club, get to know good breeders, see how they do it, offer to give them a hand with litters ect in exchange for advice and experience, get some good stock, well bred females to breed from (and males obv!) start small with just one or two litters a year, and see how it goes. What colours would you want to breed? Most breeders specialise in a particular colour, or pattern etc, and then aim to improve that line. So you would need to know what traits are needed to make improvements to your own stock. Where would you advertise etc. . . Also make sure that you have a contingency, money put by for vets bills, extra cages for hams that dont sell, or perhaps get brought back to you. f mum dies and you have to hand rear a litter, would you have time to do feeds every hour etc . . .would you be able to make the changes within your life so that you could fit around them if they needed you.(take time off work, stay up most of the night etc . . ) All stuff to think about y'know
As for a small business such as a pet shop, I would start by researching on the net and going to the bank, they have lots of schemes to help small businesess, find out what you would need to do to borrow the money etc, and start building up your business plan. Find out about what insurances, rates for premisis, running costs etc are expected for a small business such as this. Good luck with it all