five stocks. no wrong answer.
you're overthinking this. there are only two questions that matter for your first roll: do you want color or black and white? and how much light will you be shooting in?
answer those two and you've narrowed it to a handful of stocks that all look great. everything past that (grain, contrast, 'the look') is preference, and the only way to find your preference is to shoot. so grab one and go.
the other number you'll see on the box is the film's speed, its iso. it just tells you how much light the film wants. a 200 or 400 speed is the flexible middle, which is why every stock below sits there. faster film (800 and up) is for low light, slower film (100) is for bright sun and maximum detail. you don't need to memorize that yet, just start in the middle.
the safest first roll there is. warm, forgiving, cheap, and everywhere. it makes an ordinary afternoon look a little golden, which is the whole appeal. load it, shoot in daylight, and don't think about it.
gold's faster sibling. same warm, familiar color, but the extra speed handles shade, cloudy days, and indoors with a flash. this is the film your parents shot on family trips, and it still just works.
the upgrade you'll want eventually. gorgeous skin tones, soft color, and a wide exposure latitude that forgives your mistakes. it costs more than gold, and for portraits it's worth every cent.
the black and white standard, and has been for decades. contrasty, grainy in the good way, and it looks right on almost any subject. if you want to shoot black and white, start here and don't second-guess it.
the night film. it's balanced for tungsten light and glows red around bright lights, that halation you've seen in neon photos. it isn't a practical everyday stock, but for a city after dark it's unforgettable.
there are dozens more, and you'll get to them. hp5 plus if you want a softer, more flexible black and white. ektar 100 if you want maximum sharpness and punchy color. fujifilm superia if you like cooler, greener tones instead of kodak's warmth.
here's a rule of thumb while you're starting out: buy two or three rolls of one stock, not one roll each of three. shooting the same film for a while is how you learn what it actually does, and it's cheaper per roll anyway.
none of them are wrong. the Film Stock Field Guide breaks down 13 stocks with shooting tips and dev notes for each, so you can see what a stock actually looks like before you spend money on it.
a few things you don't need on roll one, whatever the internet tells you: expensive 'pro' stocks, expired film (a fun experiment later, not a first roll), and pushing or pulling to non-standard speeds. shoot a normal stock at its box iso in normal light. get a clean baseline first, then go get weird once you know what normal looks like.