Hi there, welcome to UK-Y

. Good luck with your plans.
Hi, I am new to this forum and I didn't see an introductions section. I apologise if there is one.
You can introduce yourself in the
Welcome Wagon section

.
I have some specific questions regarding moving from the US to the UK. How complicated would it be in terms of legalities to get there, and the differences in things such as taxes, licences and regulations once there?
It depends on what you want to know, really. If you are a US citizen you must always file US taxes every year, no matter what country you live in. However, you should not actually have to pay any US taxes unless you earn above a certain amount each year (currently the equivalent of about $90,000) - however, you will get taxed in the country you live in (i.e. the UK).
Licences - do you mean driver's licences? If you have a US licence, you can legally drive in the UK for 12 months after you move. However, in order to drive after 1 year, you must pass all the UK driving tests as if you were a new driver. If you do not have a US licence, then you cannot drive alone in the UK unless you have passed all the UK driving tests.
To make things simpler, I am a minimalist and have been living with only a computer, two bicycles (one full size for off-roading and one folding for commuting and public transport), and about two totes worth of clothing, kitchen items, bedsheets, toiletries, etc.
I use bicycles and public transport to get around, and use a large backpack to carry groceries, or travel items, or survival items when camping. I own a couple of dagger-like knives for self-defence but no firearms or large knives/swords (are they regulated? How to import them?).
Moving stuff is fairly straightforward - you either pack things in a suitcase to take on the plane, ship your stuff using an international shipping company (but this can be expensive) or leave your stuff behind and buy new stuff in the UK. Not sure about knifes though... there have been some big problems with knife crime in the UK lately and there will likely be tough restrictions on importing knifes.
I have time to plan this descision, I am 17 years old and do not currently have a driver's licence, credit card, or insurance. I rent a flat from a relative, work at a low-paying job and will be going to college (university) next year.
How would someone in my situation go about preparing to live in the UK? And what major differences or complications could arise?
Moving to the UK is not easy - you need to qualify for and apply for a visa to live in the UK and there aren't many options. You may find it will be a few more years before you can qualify for a visa to live in the UK (or you may find you can't live in the UK at all, because you don't qualify for any visas).
As you're only 17 at the moment, the easiest option would be to get a student visa to study for a degree in the UK (very expensive though as it will cost about $30,000 per year for international student tuition and living costs and you need to show you have access to at least 1 year of tuition fees and 9 months of living costs in order to get the visa). Or you could study at a college in the US and do a study abroad exchange for a semester or a year through your US university.
Also, if you are currently a US college student or have recently graduated from college, you may qualify for a BUNAC Intern visa, where you can spent up to 6 months in the UK (but no longer than 6 months) doing an internship.
Other visa options include:
Tier 1 work visa for highly skilled workers: you need to get 75 points to qualify - for age, qualifications (minimum of a bachelors degree is needed), and earnings (high earnings are needed - if you are under 30 (20 points) and have a bachelors degree (30 points), you need to have earned at least $59,000 in the 12 months before you apply to get the other 25 points).
Tier 2 work visa: work visa sponsored by a UK company. Very difficult to get because unless your skills are listed on the Jobs Shortage list, a UK company cannot hire you unless they prove that they searched the UK (60 million people) and the EU (500 million people) and couldn't find anyone suitable for the job!
Marriage to a UK/EU citizen: only viable if you're in a relationship with a UK or EU citizen and wish to get married to them.