Hey Sciela!
There's a ton of potential answers to this and really, the only one that's right is the one you find for yourself. I think I'll start with the end of your questions first, because it's more important than the tech side of things.
It's really good that you start to hate the things you work on, it means your mind is trying to grow artistic objectivity; the kind that helps you know when something is really good. Right near the end of any project cycle I get frustrated and think I've screwed the whole thing up. ChemicalSeb and I were just chatting about this the other day. If you could draw a graph of confidence from the start of a project to it's completion, for me, it would be this hilarious mountain range looking thing where I think I'm on top of the world and then it just plummets when I start to make revisions.
All of that mental anguish is good though, and confidence grows. I've done a lot of jobs in my life. I've worked in corn fields, I was a cook and dishwasher, I've demolished and remodeled houses, but all of those things are mostly battles with external elements. I think creative work is often difficult because it has so much to do with the self, and wrestling with your own abilities. Writing music is very much internal. Ira Glass spoke eloquently on this topic in This American Life:
For the first couple years you make stuff, it’s just not that good. It’s trying to be good, it has potential, but it’s not. But your taste, the thing that got you into the game, is still killer. And your taste is why your work disappoints you. A lot of people never get past this phase, they quit. Most people I know who do interesting, creative work went through years of this.
(Coincidentally, his cousin Philip Glass is one of my favorite composers.)
Now moving onto the first bit of your question. There's a lot of fairly affordable software out there to get the job done. For the kind of stuff it sounds like you want to do you'll need
- A Digital Audio Workstation - Usually a multitrack digital editor that you record all your music with.
- A MIDI Keyboard - Used to play the virtual instruments in your workstation
- A few good starter plugins
For music composition a fine start is Cubase or Logic Pro for your DAW. Those come with plenty of fun plugins to start making stuff. To use the kind of orchestral plugins you're looking for you'll want a USB MIDI Keyboard. I think the Oxygen series does well to begin with and you can usually find used ones for good prices.
A good beginner orchestral library is Garritan Personal Orchestra. Their website also had a fantastic community to learn arrangement and orchestration techniques.
Hope all goes well and you get to get some of those ideas out into the world!
EDIT: Audacity is a totally free DAW that's good to get a basic working knowledge going before you put any money out there.
EDIT PART DEUX: If you happen to be a student, the website "Studica" has absurd deals on software and equipment.