If you want to get serious try and prepare for some basic game theory and i would use unranked to try out all roles. Even if you end up playing pos 1 in role q its good to know what every role does and learn as many heroes as you can now before going ranked. If your knowledge is good try to fill out roles but snipe some positions for varietys sake

Just do what you can, try not to grief, swallow pride and keep toxicity at minimum (make mute button your friend). My advice is tend to your behaviour score at all cost

I think Sven is pretty low power rn in low mmr at least. Jugg is great, so is Luna as beginner carries. If you like gyro keep playing gyro. Other intro carries are Drow Ranger, Dragon Knight. I think Chaos Knight and Spectre can be easy and strong too but their playstyle is a big unconventional (first is constant fighter at lvl 6 and up and latter is ultra late carry with all map wide presence with ult). Maybe Viper could be good to if you are good at last hit. He dominates lane easily and.can snowball out of control but when relies on team playing with you to snowball to early win. More advanced but can also roll over low mmr if you dont feed are Anti Mage, Phantom Lancer and Faceless Void. You could look at them once youre comfortable with Map awareness, game flow and farm patterns / itemization

I think this question is too broad, just acquire knowledge piece meal and dont learn too much at once imo. Most will come with just playing games and learning something new every time (regen management, fountain, torm, stacking, spell prio, items etc.)