Yeah those are some nice sites and it's good that you're aspiring to that style of website design! I can tell you that whilst reselling web hosting can make for a good passive income, if you don't know what you're doing it can cause you a lot of frustration. Half the battle is finding a good hosting company to partner with. Ultimately, if something goes wrong and you can't fix it, you are at the mercy of their technical support.
In the past I had a project whereby the clients wanted to move their website onto my servers. I wasn't overly experienced at the time, and I had to deal with the company who was (and still is) hosting their website. Naively I thought this would be a simple process, but it was made clear to me at the end that their only goal was to maintain their hosting contract with my client. They delayed at every step of the process and were blaming me for their incompetence, which for whatever reason, they believed and I lose the entire project. That was probably one of my most stressful weeks ever, in my life. It's not fun to have the CEO phoning you up demanding to know why nothing has happened for the past week and you have to sit there and try to explain to a technophobic businessman that you are unable to gain access to the back end of their current website and that the back up files of the website, given to me by the other hosting company, was in fact a completely different and non functioning version of their website. Yes, sabotage was on the menu that day...
You'll have to learn a fair bit about how to manage a domain and the DNS entries of it, how they all work and the least destructive way of transferring a website. Something else I have come to learn is that surprisingly, instead of simply contacting someone about a new website, they go off and buy the domain name and start using their shiny new emails immediately. Some times they've already signed up to some kind of hosting package, in which case you have to try and explain to them why it would be better for them to have everything under an account with you. Good luck if they've just signed up for a year!
Oh and be expected to answer questions like how to make titles bold in MS Word!
But it's not all bad. Once you've got the understanding you can make some decent income from it, and you often become their go to person for any other type of technical or design work and some times this can be invaluable. But it would be unwise to treat this is a very simple aspect of website development that doesn't require much input on your behalf! I would suggest perhaps working with someone else with experience in this area if you wanted to then go off and do it for yourself. It's best not to use your clients as guinea pigs!