Hi, here is some advise I got when I like you started:
I have made the advise in three parts; first part is Generel, second part is for the Domain, third for the Hosting and the third.
Generel
1. Make goals to where you see yourself in this domainbuisness in 1 year, 3 years, 5 years and 10 years. BE REALISTIC.
2. Split your domain investing in parts; for short time investment and long time investment.
3. If you dont plan to park the domains (why should you, with your experience in webdesign)

So make a unique website for each of your domains. With unique I mean between your own domains.
4. Make a plan for each of your domains. Park, minisite or unique site, decide before you buy the domain.
5. If you want to make a unique site, then develope a concept for the domain.
6. Market your domains through joining forums and smoothly drop in your links to your domains.

This is the free mode style
7. As soon as you have bought each domain, submit your domain to Google, Yahoo and DMOZ, and all other search engines you can find.
Domain
1. stick to .com, until you have experience.
2. No Numbers in domainname.
3. No Hyphens in domainname.
4. MAYBE THE MOST IMPORTANT ADVISE, STAY AWAY FROM TRADEMARK DOMAINS!
5. Be sure that the domain, is REALLY pronounceable

6. If the .net and .org also are free, then take them too. THIS ONLY replies to the domains you want to make a unique site to.
Hosting
1. Do not host at UNLIMITED EVERYTHING hosting companies, the only unlimited thing they give is there lies.
2. Be realistic, do not expect millions of visitors right away, so in many cases you dont need a lot bandwith/space in the beginning.
Well for now this is what I can remember, maybe I will come back later and add some more.
I hope this is helping you.
Good luck with your domain investment and best regards...