1- Indeed our society and our economy have become very materialistic. While it is permissible to start a business in the areas you mentioned, if you want true Barakah in your life, see if you can start a business in more beneficial areas—such as basic necessities or areas human beings can benefit from for their self-development. But as long as the products are halal, from a Fiqhi perspective it will be halal to sell them, even if some people misuse them or become excessive with them. My recommendation is for you to study what people reasonably need and then create a business to address those needs. This would be better than inventing “new needs” which “create new desires” for people.
Furthermore, try to ensure that your business does not cause significant harm to the environment and does not lead to the unnecessary wasting of resources. So yes, we must try as best as we can to save resources and not be involved in wasting them.
One recommendation is to come up with creative methods to raise awareness. For example, you can print a label on your products and remind the consumers “that resources are precious and limited, so please don’t waste this product. Use it wisely, as millions around the world do not have the luxury to afford such a product.” It really does make a difference when people are reminded.
Yet another recommendation is to be creative and find new, environmentally-friendly ways to generate clean resources. For example, since making a pair of jeans requires so much water, have your business come up with a way to recycle water, or use properly recycled water to make the jeans. This will require more effort and possibly decrease your profits, but Allah will reward you for that. Also, today there are people who want to support environmentally-friendly businesses, so be creative with your marketing and you can be successful. So any way to offset the damage causes to the environment will make your business more and more ethical.
2- Wealth and comfort are not discouraged as long as one guarantees that materialism will not negatively affect him and weaken his faith. However, one must also not be extravagant and wasteful.
3- Initially you might have to partner with existing businesses out there (that may not be so ethical), but as long as your intention is to establish a fully ethical business, then your pursuit is justified (just make sure no haram is committed). So just have the goal of: trying to be creative and save resources, try to decrease the impact on the environment, and your pursuit of a business in the textile industry will be justified.
4- Honestly, buying a very expensive and luxurious car is not recommended and not called for. Even if one is rich and paying his religious dues, it’s unnecessary to spend so much on a car. Instead of driving a $300,000 car, the rich person can drive a $50,000 car and do something useful with the $250k. True believers avoid extravagant spending.
5- You are free to set the profit margin as long as you are not engaging in any deception of the buyer. Yes, Islam recommends one not to make too much profit from customers. Doing so usually leads to greed and exploitation of people. So the profit margin should be kept reasonable and Allah will put more Barakah in the business. You are not obligated to inform the customer of your actual costs. As long as you are not deceiving or lying to them, you can set whatever price you want.
6- It’s permissible to sell items with quotes and names of our Imams. Just make sure they items are not the type that would usually be thrown in the trash. So for example if you want to sell a cup, you can have a hadith written on it about remembering Imam Hussain’s thirst, or about thanking Allah for blessings. That’s fine. If you suspect that usually such items become najes, you can write something like “The First Imam states….”
7- Those hadiths about selling knowledge basically refer to those who misuse the knowledge and do not follow the instructions of Ahlulbayt (a). Let’s say I use the knowledge of the Imams and sell my book, and I use the money in haram or not in God’s obedience. This is condemned. But let’s say I use the profits to support my family, to support charities, and so on—then it would be ok.
8- If you know that the majority of people will use the fashion items for haram (wear them publicly), then do not be a part of such business. For example, let’s say you know that 90% of your customers will wear those leggins publicly—in this case avoid selling them. As for the knife example, usually people use it for halal. It’s rare for people to use to kill others. Let’s say you lived in a society where 90% of people used knives to kill unjustly—in that case you should avoid selling them.
9- What you can do is narrow down your market areas. Try to sell your items in areas that you know they will be misused less.
10- You can get the opinion of other scholars on these questions. No problem in that. And you can post my answers on other platforms. That’s ok.
May Allah bless you.