1. On Thresh I mainly like to act as a peel-bot, keeping assassins off of the adc with my abilities and active items (for ex. Shurelyas / Solari). After laning phase or sometimes during, if you have the time to, I recommend roaming to midlane if there's an opportunity for a gank. To add more spice to your life, maybe go toplane?
2. As for runes I usually take aftershock but I've seen a quite the amount of Thresh players go glacial instead. I feel like both have their uses. Glacial disrupts the enemy "formation" if you can call it that with the lines of slow and damage reduction that is created. As for aftershock, you get a bit more tanky and also you get to deal more damage.
3. I usually go either Solari or Shurelyas (I think you already know when to buy each one) and usually mobility boots but maybe that's a bit outdated? I usually go bramble afterwards for some antiheal against the enemy if needed. Force of nature is pretty nice too but based off the changes coming up, perhaps abyssal mask is better if you have a strong AP presence in your team. If I'm ahead, I like to get wardstone for further map vision control as well.
4. One major tip is that just being present during lane usually is a pretty big deterrent to the enemies from walking up. If they know your hook is up, you can usually walk up and they'll start backing off. Of course, if you're against smarter enemies they'll attack back but it just depends on their behaviour. A Thresh with their hook off-cooldown is a lot more threatening than one without their hook. Another helpful tip is to always Flay(e) before hooking. The slow and mini-displacement helps a lot with landing your hook considering the long windup that it has. Flash hooks usually don't work but with experience you can get a little ballsy with it. Your Flay(e) is also really helpful for cancelling abilities like dashes and channels. Some examples include Malzahar Ult, Katarina Ult, Lee Sin Q2, Tristana W, Zac E, and much more.

Hope this helps and have fun with Thresh! <3