What are the things required while modifying nopCommerce and lauching the modifies website ?

First of all is it legal to use nopCommerce and modify it according to the needs and use it for commercial purpose ?

Lets say the modification is done and the website is ready to launch, what are the things that are required to be done in order to launch the website ? Do i have to make any registration of my website with nopCommerce that i am using there project kit as reference ? or i have launched a website which is initially developed with their project ?
I have to pay any monthly fee to nopCommerce ?
Other than "Powered by nopCommerce" which is on all the webpages, is there anything else i cannot remove unless i buy the license fee ?
and if i buy the license fee which is i guess $50, this is a 1 time fee ? or annual fee ?

First of all is it legal to use nopCommerce and modify it according to the needs and use it for commercial purpose ?
Yes

Lets say the modification is done and the website is ready to launch, what are the things that are required to be done in order to launch the website ?
Just publish it

Do i have to make any registration of my website with nopCommerce that i am using there project kit as reference ?
No if you have "powered by nopCommerce" on each page of your site

Other than "Powered by nopCommerce" which is on all the webpages, is there anything else i cannot remove unless i buy the license fee ?
No

If i buy the license fee which is i guess $50, this is a 1 time fee ? or annual fee ?
One time fee

thanks a lot my friend for the information...