1)100shirts per design is consider limited or not?
Yeah, I would consider that pretty limited.
2)if it is how much is the market price for a limitations?
I'm not sure if the market price is really dependent on limited editions. If that were the case, Affliction and Ed Hardy couldn't sell t-shirts for $50-150.
That said, your marketing, branding and distribution will determine the perceived value of your shirts. Once you know that price point, you can possibly upcharge for limited edition designs, if your target market is the type that would support that feature.
3)screen printing or dtg?
Screen printing is considered the best quality if you are looking to compete in the retail market.
4)the best quality type of tshirt?
It's really up to you and what would best attract your target market. 100% combed ringspun cotton seem very popular these days. But some like 50/50 cotton poly, some like bamboo, some like organic cotton. As for fit and style, some like a fashion fit tee, some like heavier, bigger fit tees. Maybe you can figure out what your retail competition is and see what they are doing.
5)whats the best method of marketing??
Having a big money budget to launch a nationwide marketing and branding campaign.
If you don't have big money, then you need to really isolate your target market. Figure out what they do, where they go, what sites hey visit, what magazine they read. And then focus on getting your brand in those areas. It's all about getting exposure and traffic to where your shirts are going to be sold.
6)more designs for men or women?
Depends on your brand.
7)20 designs for starter is too much or too less?
Seems like a good number. But it also depend son your brand and market. For instance, if you are targeting a specific niche, then a few good designs directed to that niche may be enough. But if your brand is targeted to a wider retail market, then having a good number of design options increases your chances of converting sales.
8)do i need to copyright every designs or just my brand name and logo?
Designs are technically copyrighted once they are in fixed form. So it's not needed to officially copyright them, unless you really wanted to. Brand names and logos are eligible for trademark, not copyright. In my opinion, it's much more important to trademark your brand name or logo rather than copyrighting your designs. But federally registering a trademark is something you should do when you can affird to do so. Don't spend money on legal, when you should be focusing on marketing and production. Remember, your trademark will not prevent infringement, it only gives you the legal recourse to take action against infringement. So if you are not prepared to file lawsuits, then you can wait to register.
