Is completing the Bonus Objectives in Threads of Fate the only way to earn Renown while leveling? Beyond the 60 boost, of course. As a test I queued up for a random dungeon after picking up all four zone dungeon quests and neither the dungeon or the quest turnin gave a Renown, and it doesn’t look like the zone quests (Bolstering Bastion, Support the Court, etc) give Renown either.
Also, the 20th and final bonus objective I completed in Ardenweald didn’t give a Renown either which I thought was odd, especially since I had earned it spread across 3 different covenants to try to maximize my Wisps of Memory collecting. Yeah yeah, I know it’s late to work on table stuff, but I want to level the rest of my alts to 60 before Dragonflight anyways, so I may as well get some extra gold and pet charms out of it while I’m at it right? 
tl;dr Can you earn more than the 19 renown from bonus objectives while leveling, or is that it until you hit level 60?
Did you buy the renown boost to 60 or whatever it is? You should get enough to almost hit 80 by the time you hit lvl 60. Never counted how many you get from bonus objectives. I’d just do torghast daily and go along with the objectives and got far along on renown on my last alt I leveled 
Yep, I got 4 of the 60 tokens to get all 4 covenants to 60 to start. I’m not as worried about hitting 80, but if I can hit 67 or 76 on multiple covenants while leveling that’ll get me more Wisps of Memory to give my table a jumpstart once I hit max level. After that I don’t really care about renown on the alts anymore.
Just trying to be efficient haha.
If I just keep leveling like usual through the bonus objectives for renown plus gathering/questing etc that’s cool, but if I can do something else to also earn a few more renown while I level, then I’d add that in as well. Like, I heard Torghast gives renown, but only at higher tower levels which I don’t think you can do while leveling up?
Don’t quote me on it but you can do the ‘daily’ and if I recall, for me at least, I’d get a renown from it. They did changes since SL launched but renown has always been a weird thing for some people. [No you can’t do higher floors/layers while leveling].
I don’t think there is too much variation when leveling with regards to renown. But you should get 70 or so if you did the renown boost at lvl 50 or whatever. Just not through dungeons, those were shown to be reaaaaaally wonky.
You can get renown from dungeons, bonus area quests, the zone quests and the Torghast quest.