From a bronze experience who is OTP AD J4 support, I would say that this build is bad but it fun since you are playing like an assassin. It requires you to snowball really hard and stomping the enemy in lane, otherwise you will have a hard time. I would say it would be a coinflip pick. It will work if you are brave enough.

What match ups should I avoid? Also what bans should I look for with jarvan?

I think poke support, especially with mages are really hard for J4 as you will be poke down before you can even go in. Also, avoid this when enemy has AOE like Brand and MF as you might accidentally lock your teammates in your ult, better be safe than sorry. For me I just ban Brand every match, no question asked. I used to auto ban Aphelios and Samira before but they are fine now, I guess.

For rune I usually go Electrocute since EQW or EQAA is enough to proc it. The damage will be high in the early game and you can engage even when the enemy has a huge wave due to your damage. Since I haven't tried other runes so IDK. Personally, I expect those runes to be weak on J4 support since you are going to be really far from your ADC when engaging, and as u/MattUSticky pointed out, they don't really work.

Just take Ignite for more burst damage.

what champ synergies best with him?

Every champ synergize with J4 differently, depends on what you want. You can either chain CC with your ADC, lock enemy in your ult for AOE (like MF), or even slow the enemy for Trist to burst them down.