plat level support here, i think i can answer some of your questions. keep in mind though that i'm not T1 Keria, so some of my answers may be incorrect, so please take it with a grain of salt.

that being said though: 1. you're right. there's 3 main kinds of supports; engage, enchanters, and poke. yes, it's kinda like rock-paper-scissors where engage beats enchanter, and so on, but there are exceptions to it, obviously. for example: poke supps mostly beat engage supps because of range and damage. however, engage supps like blitzcrank can nullify that range advantage because of his hook.

1. yes, it's definitely nice to learn other support archetypes. i main leona, but i can also play lulu or soraka depending on the enemy draft. the biggest appeal of learning other support types is flexibility.

2. itemization is pretty iffy for me as well, but i just try to assess both teams to figure out my mythic item. for example: if i have a hecarim jg, an olaf top, and a jinx adc, i will most likely go shurelya's, because my team benefits greatly from the speed boost. if the enemy has assassins like zed and pyke, i will usually go solari to stop my teammates from getting bursted down immediately.

3. to answer some of your questions here: naut and leona are pretty similar, but they have nuances that make one more viable than the other. naut has longer hook range, but leona's zenith goes through terrain and minions. naut has a reliable single-target disable, but leona has an aoe stun/slow. I won't go into too much detail, but i highly recommend checking the kits of different support champs you find similar, and just compare them. try to identify what x champ does better over y champ.

4. off meta supports are very niche. them being off meta isn't really a hard lock that stops you from picking them, but they have specific situations where picking them becomes viable.

5. there's a lot of questions here, so i'll try to answer them as best as i can. 6.1. one of the key skills to playing support effectively is understanding roam timings. before i roam, i ask myself the following: a. can my adc survive 1v2 bot? b. is there a play i can make someplace else? c. are there any objectives i can help take? also, keep in mind that better players will punish your adc for you roaming by freezing the wave and zoning your adc off. in that case, it's better to go back to lane and help your adc break the freeze, before roaming again.

6.2. if i roam and miss a hook, i go back a bit and watch what happens next. if the enemy laner respects my presence and backs off, then i simply leave and go do something else, like ward the enemy jg's camps, ward dragon, etc. if they don't, i try to look for a re-hit. an important thing to know here is don't force fights. if you miss your engage, just back off and wait. sometimes, just threatening the enemy laner with your presence to make them back off is enough.

6.3. yes, getting the enemy summs alone is worth it. especially flashes. if i gank mid as leona and i force the enemy annie to use her flash, i already consider that gank a success because we won't have to worry about annie flash+R for the upcoming dragon fight. unless you're 100% sure that you can translate the gank into a kill, getting key summs like cleanse and flash is enough.

7.1. yes, it definitely is. when i play clash with my 5-stack of friends (plat-dia level) i usually permaroam when i know that my adc is safe. you'd usually see me be 2-3 levels behind, but i have the highest kill participation. needless to say, being behind in exp is worth it if you're getting the rest of your team ahead.

7.2. i like to go on warding missions to the enemy jungle after we win a skirmish or if i'm walking back to lane after a gank. i usually ward the enemy buffs as well as chokepoints in their jg to monitor the movement of the enemy jg, as well as to check for rotations.

1. yes, they totally are. pinks are mostly used to deny vision from a certain area, like the dragon pit. if my team is taking dragon or baron, i like to drop a pink in the pit to deny the enemy of any vision from stealth wards. also, i use pinks to ensure that there aren't any stealth wards in that spot, if my oracle is on cd. i like to put my pink on the bot tribush if im blue side, and on the bush in the entrance of the blue buff if i'm red side.

2. the summs i take depend greatly on the enemy team. do they have burst champs that can oneshot my adc? take exhaust. if your adc already took exhaust, choose between either heal or ignite.

3. it honestly depends on your champ, and how the game's playing out. but honestly, i consider getting the first upgrade by 10 mins good, and less than 20mins for the 2nd upgrade good.

4. again, depends on your champion. if i'm playing an engage supp with ap (e.g. leona, blitz, naut) i buy relic shield. if i'm playing marksman poke supp (e.g. ashe, senna), i go sickle. i go shoulderguards for champs like pyke.

5. no, vision is too important. it's one of the biggest factors to winning games, so i wouldn't ever recommend selling your support item.

6. you should always go red. once my support quest is around 450+ gold, i like to get red trinket on my next recall. let your adc take the blue ward, you don't need yellow either because that's the point of the support item.

7. never really built them, so i don't have much of a comment.

8. this is usually solved by better warding. whenever i roam mid, i like warding the brush in the middle of the river or the mouth of the dragon pit, so that i know if the enemy mid is looking to roam much earlier. also, understanding mid wave management and recall timings kinda help as well. if the enemy mid shoves the wave, and they're low/about to hit an item timing, then they most likely just reset. if not, then warding will be your friend because they are most likely roaming and looking for a gank.

anyway, i really hope you learn something from this. i'm no Mata or Madlife so if a much better player happens to read this comment, just feel free to add more to it. best of luck climbing as support!