1- I can't think of any reason not to list your domain right away. The only small exceptional hiccup I can think of is the transfer lock limitations. While I don't think there are any on new registrations, I really don't hand register many domains at all so actually am not 100% sure. Regardless, even if you buy a domain from someone else and change the whois information which does result in a lock, then that lock is 60 days. Transfer lock essentially means you can't change registrars during the 60 day security period (mainly there to prevent theft and hijacking of domains).
2- Depends on where you sell the domain. Obviously a website with content usually has more value. However that also requires a lot of time/money invested to create the site and more importantly the content. I think it's safe to say that most domainers would tell you to not develop a website (unless you're super good and fast at doing it yourself). Another factor is that domain buyers usually come to buy your domain because they already have a project in mind. If their project does not match up with your content then all that work would have been for nothing as they will place zero value on the content you created. Plus they might actually think the site is not for sale if they see content on it. For the final answer, like most domain questions, it really depends on the specific domain, but I'd say as a general rule of thumb, it isn't an efficient use of your time/money to develop your domains.
3- GoDaddy Auctions is a good place to start.
@NameJetGM and
@DropCatch Support also have auctions of caught expired domains. I'd definitely invite you to follow my blog either directly at NameCult, or here at NamePros (the links are in my signature), every day I list a few hundred of the better expiring domains going to auction each day, as well as several hundred domains at closeout (instant $5-$11 buy it now prices aka no auction)
4- For your taxes it totally depends on where you live. If you are just starting with a handful of domains you might not even need to bother reporting anything until you've earned a minimum of profit. That being said .. this isn't the best place to ask for such advice as what applies to one person won't apply to most others.
Hope that helps a bit .. good luck to you going forward!