Since i'm new with this, i'd like to be able to experiment and get used to the engine, BEFORE I start using the fancy stuff. Is it possible for me to start my free trial later on? I'd appreciate any quick answers, because i'm waiting on the registration page.
I'm pretty sure you can. I'm running the free version without any trial - and yes, i can activate the trial online (Just went through the motions now).
I believe you can just use the free version of Unity, then re-enter a new serial later for the 30-day trial of the pro version. I did this after roughly 5 days of the free version and it never caused me an issue.