Hello! I can answer some of these for you.
How to get the best or Top armor needed to start properly the next Expansion? - To get the very best armor offered in the game, you would need to complete Mythic difficulty raids, or do high level Mythic+ (commonly shortened to M+) difficulty dungeons. There are plenty of ways to get good gear that don’t involve the highest level of content however.
Your first goal once you hit level 120 should be to get into the Nazjatar zone (only reachable at lvl 120), and start working towards getting Benthic gear. I’ll leave a link here on how to get to Nazjatar, and another one for Benthic gear for you. From there, you can fill out the missing pieces of gear through a combination of world quests, low level M+ dungeons, or pvp.
https://www.wowhead.com/guides/comprehensive-nazjatar-guide#how-to-get-to-nazjatar
https://www.wowhead.com/guides/benthic-gear-effects-nazjatar
How to get the best Weapons? - One of the first quests you will do in Nazjatar will award you an ilvl 370 weapon. This is far from the best, but it will give you a good start. The world bosses in Nazjatar have a good chance to drop ilvl 415 weapons (killable once per week), and filling your conquest bar one time in pvp will give you a 410 weapon. Other than that, it’s the same as with gear. Raids and M+ dungeons will be your best bet to get anything higher than those.
How to Achieve Flying in Draenor and now in BFA - Flying is achieved in Draenor, Legion, and BFA through an achievement called Pathfinder. If you search in your achievement menu for Pathfinder, it will give you the exact requirements for each, but generally involve gaining reputation, finishing story questlines, and exploration.
and finally How to Get those Armored T-Rex as Pets? - I’m not really sure on this one as I don’t play hunter very often, but here is a link to one of the best resources for hunter and their pets.
https://www.wow-petopia.com/index.php
As far as guilds go, check through the new player friendly guilds listed here:
Or on your realm forums which can be found here: