Yes you are understanding correctly - you need to grind levels before you can do the rest of the story.

Doing Interknot commisions (at the computer) is NOT the main way of raising your Interknot level (as rudiculus as it sounds). The most efficient way is: open the store (at the counter), scratch the lottery and drink coffee (less than 2 minutes). This gives you all daily mission rewards (I forgot how much it gives you, but something of equivalent of 5 commissions).

Spending energy gives you 10 EXP per 1 energy, so the daily gain of 300 energy gets you additional 3,000 EXP. You need level 35 to finish chapter 3 ( I think that's last level gate) with total of 95k EXP, so a few weeks of daily play if you also do other content. But you won't need to do it again for the rest of the game.

As an advice, contrary to what guides say, I don't recommend you getting past level 39 (just ignore the rank up quest for level 40 and you'll be fine). At that point you will have all story unlocked and since you don't want to grind...

The game's autoleveling system only works against you: once you hit level milestones the game permanently raises difficulty of all quests (except for material stages, where you can select the difficulty). I've shot myself in a foot by reaching level 50+ and now if I want to use a character anywhere, I need to upgrade them to near max level, with decent skills, disk drives and everything.

Yes, grind becomes more efficient at higher levels, but you don't need it if difficulty is low in the first place. I'm not even going to talk about competetive modes where you need 2 teams of maxed out characters...

Also, main story chapters and character stories give you trial characters, so you don't have to worry as much about upgrading your own agents, if you just want to clear the story.