What kind of time and money did you have to spend on getting that site ready so that it could be sold? Did you have to aggressively market it so the prospective buyer could see traffic patterns? Seven months seems like a long time (to me) but if your profit margin is high and you have the patience, like it sounds like you do, then it would be worth your time.
It depends upon the type and PR of the domain name. I had seen many people buying domains for cheap prices and selling it on sites like sedo and earning quite a profit. It depends on how much you are lucky to choose a domain name.
I don't think there's much advantage to building a site if you're sole intention is to sell the domain name. What you use the site for is normally not what the buyer wants it for. They aren't after your content, just the name. You may have purchased a name because it's a nickname or sounds cute. The buyer wants it because they just wrote a book by that name, etc.
The domain name is nothing to shout about, I’m not even sure if it’s a good investment. I can't give you any promise as it's or just treating it as a hobby or.. ? Do you even have the time to develop it?
domain which I’ve back ordered last year has dropped and was successfully captured.
As of now all generic domain with dot com extension have been registered. But there are still relevant two and three domains that you can register and flip it for a small profit. Just make sure that the domain is in demand and don't register a domain because it sounds cool.
If you have a generic and aged domain you can easily flip them for a profit. But don't expect to make a lot of money from newly registered domain simply because they are new and it does not have a good reputation(PR/Backlinks/etc) from Google.