Hi!
Well, I don't know how many people actually populate this forum these days (apart from spam bots).
On the bright side though, I'll try to answer your questions, even though I'm a lowly newbie

First thing - Sibelius is not a DAW (Digital Audio Workstation). Cubase IS a DAW and if you're planning on composing music using digital sample libraries such as EWQL Gold, you'll need a DAW to actually "perform" your music, not just write notes. I too use EWQL Gold and FL Studio 9 as DAW and you can check out my website for the results (granted I'm not the best guy when it comes to mastering and post-production, but the difference against Sibelius is - IMO - easily noticed.)
Secondly - I'm sure there are trial version of software like Cubase or other DAW (Sonar, FL9...). Just google it, I think you'll come up with many hits.
And finally - to your work - it looks like a good piece of music, but it would really benefit from better sounds (that is, it needs to be produced using something like Cubase). But it does have a nice flow to it...
By the way, I'm from Slovakia, I study in Brno, check out my website (scigulinsky.ic.cz) there's a way to contact me, so if you'd like any other ideas or advice, be sure to let me know (since this forum seems to be quite dead at the moment.)
have fun.