How do I go about perusing a career in musical theatre?

Firstly - perusing means reading through. You must mean pursuing.

You can't just 'go' abroad - the USA has hundreds of thousands of unemployed actors already, so it's very difficult to get all the legal stuff to move there.

The GCSEs mean very little, apart from being a way to get into a good A Level college to get A Level Drama or Performing Arts, and after that, into a top drama school.
If you don't have enough money, you'll have to do what thousands of others do - work for a few years, saving every penny.

You'd also need several years of training at a basic level at a good acting school, good singing and dance abilities, a lot of stage experience (and ordinary school stuff doesn't count at all) as well as huge talent.

Each of the drama schools gets about 5,000 people auditioning for only 24 to 30 places, every year. It’s also very expensive – the fees alone are between £9,000 and £27,000, and on top of that you have to pay all your own rent and living costs.

And even after all that, the best you could ever hope to get is about 2 or 3 weeks' paid acting work a year - that's the average. Almost all actors have to work an ordinary job alongside acting just to pay their bills.

If you really want to try, knowing how hard it's going to be, get into a good acting school in your free time and start learning. If you progress from basic classes to intermediate and then to advanced within a few years, maybe you have some talent and could take it further.

If you join a good community theatre and you always get leading roles, again you can assume that you have talent.
After that, try to get a high grade A Level in Drama with a few related subjects like English and Psychology, and then apply to the drama schools.

After you graduate, you might be able to get an agent, who might be able to find you some auditions, and if you're really good, and really lucky, you might get the occasional job.

But go into this with your eyes open.
It's a really hard career to get into.

Good luck!

The UK is a great place to study acting. If you have not gained a place a a good drama school then work towards that. Approx two thirds of first year places go to people over twenty who have extensive performing arts experience or undergraduate degrees in something arts related. The remaining third go to high school graduates thought to have unusual potential.

"Going abroad" means that you will have the added disadvantage of being a foreigner in a country full of aspiring young actors. They have local knowledge and can study for local fee rates (as you can in the UK).

Your aim will be to develop a level of skill and experience that would be considered to be marketable by agents. Your money is insufficient for that purpose. You will be competing for work alongside graduates of acting schools there. Unless you have that level of skill and experience reputable agents will be hard to find.

Look closely at the top drama schools in the UK - consider their audition requirements, the level of competition and the fee structure. You are very young and the primary concern at these is, and always will be, that you have enormous acting potential and ability. If you have the audition fee, you will be able to audition. Remember that as there will be thousands of others wanting the same high standard of training, these schools can pick and choose and they do. They can find many young people who have shown an ongoing commitment to the arts and have good high school grades.

Research is your friend and remember that the best schools in the UK (look at the Drama UK website) employ people to answer any question about entry. Expect to work hard towards your goal here. Best of luck.