Selling Web services with WordPress, legal?

Sorry for the long post, here it goes.

I would like to start a business on the side and then go full time when the circumstances allow. I’m thinking of offering similar website features such as this company offers https://www.netministry.com/CMS_Hosting_Features.asp. I would like to do the same except they use their own CMS platform (Inspyre) and applications. Can I do the same using WordPress themes and plugins and charge clients depending on the package they choose? (lite and premium packages like the ones on the site above). I will be handling everything that has to do with hosting since I have my own shared hosting plan (Dreamhost). The themes, plugins, and features will all be hand-picked by me from the www.ads-software.com site (until I get the time to build my own stuff).

My question is can I offer such services as long as I place the required credit by the author of the theme/plugin? ie: Footer link to theme’s author website when using someone else’s theme, link/logo to plugin’s author website when required (some plugins don’t have anything referring to the author).

Obviosuly I will be offering more hosting features myself with a better plan, hence the increase in monthly price if the customers decides a better plan. This is only something basic for people that don’t have $300+ dollars to drop instantly on a custom designed website once it’s done. I will be offering other services, but they will be all me (custom website design, logos, maintenance, updates, backup, etc.)

Thank you for taking the time to read this and comment.

– Marcos