Domain name is like an address of your online business. Once the domain name is set to your server space, your website gets visible on the internet. When anyone puts the domain name in the address bar, it will redirect them to the website with the same domain name.

Yes, you can register such a domain name. But make sure you follow some tips while choosing a domain name same as your business name. Like, suppose you have registered a business name as Fresh Cakes Ltd. then you wouldn't want to pick a domain name as nicksfreshcakes.com.
But you can consider other options like :
freshcakes.com
freshpastery.com

Hyphens and Numbers can jumble your customers and hence, you need to avoid its use as far as possible. Like, if your juice bar name is 'Juice For All' then avoid using 'juice4all' domain name. It may confuse your audience making them think that you serve 4 types of juice to everyone.
Adhere to A to Z for your effective domain name.

Yes, it does affect but not at a large level. Having a targeted keyword in your domain name is a good sign of having an effective domain name.

Yes, domain registration lasts mainly from one to ten years. So, it is required by you to note the expiry date of your domain name and renew it before it expires. The free domain name that you get from ServerVendors web hosting plans remains with you as long as you are associated with the company.

Yes, you can resell your domain. Additionally, you can become a domain reseller and sell over 400 extensions and TLDs.