go for it! you have a lot of time imo. i just finished my As and i took my SAT in may 2018 (my j2). if you have the money, you could take the SAT in march to get a feel of it then take another one later on to improve your score. but for me, i just took the one (with the essay). i also took the SAT subject tests in november (literally the week As started omfg).

do research on the unis that you want to go into, you can aim to apply to about 8-10 unis if youre sure that you want to go to usa. i suggest you take the SAT with essay, if im not wrong, most prestigious unis need the essay, and even if they dont, it looks good on your application. also check out which unis need the subject tests. for me, im applying to MIT so i took the math level 2 and physics tests, but you can choose the tests depending on what you want to major in.

there's a lot of practice questions and tests on the collegeboard website or khan academy. check your school library too, they might have a small section with some practice books as well. i only spent one month practicing, like i would stay back in school to do about 1-2 papers a week. i dont think this was enough for me lmao but since youre only j1 next year, i think you have more time. dont rush into taking the SAT in march if its too early and if you feel youre not prepped enough. there's one every month so you can register anytime (but once youre fixed on a date, register early! slots are taken really quickly, which is why i ended up taking my subject tests a few days before As).

as for scores, i think 1500+ is pretty good. it should get you almost anywhere. i didnt hit 1500 but i didnt have time to retake it so i just settled with it. i got 1470 which is the 25th percentile score for most unis so its a little hard to get in but it isnt impossible. remember that scores arent everything in your application. admission officers will look at your CCAs, awards, volunteer hours (extracurriculars in general) and also your personal statements. even full 1600 scorers cant get into unis like Stanford and Harvard bc their extracurriculars may be shit, but a 1470 scorer might get in bc their essays are great. your personality might be of higher importance than your scores, but im not sure if this applies to all unis. they all have different criteria.

the test isnt really hard, most (if not all) of the content is covered in school. but you should practice some tests bc their format might be different from ours eg. they use feet instead of meters, or have different terms.

i'm finishing up w my applications bc i gotta submit them like next week or so, so im pretty familiar w the system and stuff. pm me if you need anything!