The biggest mistake I think you could make is buying everything all at once before you've even gotten started. Buy a little at a time, and little by little build your collection. I started out when I was 14 (which is only 6 years ago, im young
) on a shitty old iMac, logic express, and some bose noise cancelling headphones. I mainly spent time reading books on writing, theory, midi orchestration, working with a DAW, mixing techniques, and finding tons of tutorials online on how to do various things in music. I would mow lawns to save up for something new, eventually bought an M-Audio keystation 61, bought yamaha HS5's, got Komplete 8, saved up more, upgraded to komplete 9 ultimate when it was on sale, played around with stock kontakt instruments, asked for money for xmas when I was 15 to buy spitfire albion I with the education discount, and just kept going from there, little by little, but mainly learning how to use what I already had effectively. Once I got my first job, I would save up money specifically for music and every few months buy a new library, new gear, etc. Eventually saved up to build a powerful PC for creating MIDI Mockups, got Composer Cloud X with the Edu pricing for 15 dollars a month, and now I pretty much have all I will ever need. Sure theres always new cool products that come out, but the tool is not what makes the music good. If I were to go back now, I can probably make a pretty decent sounding mockup using Kontakt's stock library. it would be limiting and take a good amount of work to execute, but its doable. a professional violinist can make a 100 dollar violin sound like a 10000 dollar violin. its all in the player/composer.
id say start with something basic. get a decent starter orchestral library, a daw of your choice, some decent headphones or monitors, a decent computer, and go from there.
cheapest route: get composer cloud, audio technica m50x's, and build or buy a computer with atleast 16 gig of ram, quad core processor, and 500gb-1tb of ssd space. that would be more than enough to start out. a basic hollywood orchestra template with single mic positions should have no problems running on a machine like that. I created a template that has all articulations I commonly use for every instrument, but all channels deactivated when I load the template, so that I can load in the instruments I want as I need them. with all basic articulations loaded for strings brass winds and percussion just using hollywood orchestra and no other virtual instruments, I think my template uses around 12 or so gigs of ram.
but more than anything, learning to write great music with limited resources is what will make you a better composer. I have a friend who did an entire score for his friends short film using just a korg microkorg synthesizer recorded into garageband. its doable.