I don't have experience but I would be inclined to say the planning stages are somewhat similar to any business in retail. Market Research, Competitors, Budget Planning etc. but in terms of bag's, you should be looking at manufacturing costs, distribution channels etc. to ensure maximum profitiability.
Would you be selling your own brand of bag or reselling other brands? If it's the former, think about brand loyalty and a catchy name along with a Unique Selling Point to differentiate yourself from competitor's - perhaps think about entering a niche as opposed to going mass market.
There's alot of things to think about, although I don't have direct experience in retailing bags, I hope I've helped a little.
Good luck Sophie!
Aspiring Young Entrepreneur
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