I even know you're 17 years old...
Brits aren't all that hard, worst case scenario (your armies wiped out) you will block the opponent with your 500 ships until he gives in, or until you build another biggest army in the world and re-invade him. You just need a good plan for all the major powers, and for each continent. For example, you want to deny Germans their unification, which is best achieved by stealing one of states necessary to do that from them, or at least helping France or Austria do that. And you want to prevent the US from ever beating Mexico, or winning the ACW later on, or winning against a rebels when they finally get a shot to overthrow their democracy. You want to control South America, best through Colombia and Brazil, and you don't want others to get access to at least the bulk of Chinese and Japanese resources, so sphere Guangxi, Yunnan and Qinghai, at the very least. In Indochina two wars should let you annex Johore and put Siam into your sphere. Controlling Persia gives you oil and a priceless ally against Ottomans and Russians. In Europe the Dutch should be your main focus, as their colonies can make someone else's industry and population a bit too happy, it's also nice to have Spain and maybe even help Italy unify to sphere them afterwards, so Frenchies have something to siege while you blockade them.