Questions regarding starting a print on demand business.

Hello guys, so for the past few days ive been really looking into print on demand and for all of those that are doing it i have a few questions:

1.For someone that is first starting with this is it better to connect via e-commerce like shopify and then building my own store(Note that i have no idea about SEO, besides the basics and only a small following on social media) or starting with etsy for example?

2.Should i focus on a niche and then creating really quality designs or is it more profitable making just a bunch of generic designs?(Basically should i go high price-small traffic or rather small price-big traffic?)

3.If its better to find a niche, how do you do that? Are there any tools i can use? What criteria should i use when evaluating if something is a niche or is simply too big?

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Thank you for all the replies.