Hamster Breeding / Marketing
Feasibility study -  Check on costs and return on the investment.  This would include start up cost like buying breedable animals (that will double as pets), cost of cages & equipment, availability / cost of consumable items like feed, treats, bedding, chewables and remedies.  Also, you have to consider that fact that you may need veterinary care from time to time. This would be provided by a specilized exotic vet, and not all areas have these in practice. 
Do you have the disposible income to invest and wait for a year or more on the return?  Profit margin, if there is any, but it is very narrow in this type of venture. In most cases it is done at a loss most of the time.  If you consider the animals, cages and equipment, and initial food and bedding as a sunken cost (you have already invested in this, as part of just having them as pets), you may see "profits" sooner.. or at least not so much loss! 
If you have to travel out of town, do you have someone to take care of the "stable" in your absence?
If you have to travel to sell your stock, does the cost of the trip make it worth your while?
Retired breeders will take up resources, with out adding to return.  Females generally hit retirement suoner then males, especially in syrians where the females must retire about 1 year of age, but could live another 3-4 years.  This is also mentioned in ethics.

Record Keeping -  This section is only relevant after you have read and completed other parts of the tutorial.
        PART 1:   Breedng records
First, keeping records of your breeding stock.  This would include pedigrees, source of the animals and their individual track record.
For the animals that you have bred and retain for breeding you will have the above info.
For specimens that you did not breed yourself, you will need to know:
SOURCE; Where they came from.... petshop? breeder? hobbyist?  If you can, how many in the litter, age or aprox age, other colors in the litter and mothers (and fathers) colors and traits on parents.  Every date and detail is importand to keep track of lines and preformance. 
When actually breeding you will need to keep track of breed dates, birth dates, number in the litter, parents of each litter, colors and traits that occur in that litter, as well as any lost pups, etc.
You will find that being able to access this info on a family or line is invalueable as time goes on.  Think of the record keeping on a long term basis and work it accordingly.

         PART 2 ;  Income and pay out records.
This is the part where you record all expendetures for ALL items and balance this against what you sell or collect.  I do not count the cost of my hamster room or the utilities used there.  However, I do count the cost of all feed, bedding, cages/equipment,  gas to transport and any other incidentals (vets, meds, preperations).
Fresh foods I use are shared by the household, so those do not get counted in eihter, but are of minimal cost.