While I agree that the transition feels a little rough, I think it has more to do with presentation and the fact that it rewrites the last scenes of the previous game and interjects new info a bit awkwardly more so than the facts and logic of what is introduced.
We're told MC needs followers because demons derive power from worship. As long as they are his worshippers he doesn't actually need them around him to live, it's more that each worshipper fuel him through I assume depth of devotion and quantity of worshippers. The more powerful he is, the more he can defend himself if he gets attacked during the war. Besides, he's made the conscious choice to forgo them and the power they bring and sacrifice his chances to live for Julia (hence why in the first game he straight up tells her that she won't like what he had to sacrifice to save her). He doesn't need to "manage without them" until the war starts and it's clear that his inclusion in the Hall of Fame is a testament of his demonic powers, which makes sense with the previously established rules since he'll gain worshippers to use in the House of Hearts and the depth of their devotion will play into how much he can do with them there to satisfy the viewers. In short, how he'll manage without them is by gaining new followers that will grow his power (and also by finding a solution to save Julia before the war starts so he can also bring them back. Plus by counting on his allies such as Astofiel, Brie, Asmodius etc. to the extent that they are true allies.)
We are still missing some details from Astofiel, that I agree with.
I generally agree, but that's what I meant when I said we needed either more foreshadowing or more exposition. The MC's survival is the a simple example of this: we're explicitly told at the start of the first game that most demons would die if they had as little energy as the MC currently had. His easy survival was considered quite remarkable. At the end of that game we learned that Lilith had been supporting the MC in some manner until he had built a base that could support him. To me, the obvious implication was that her support was the explanation for the MC's survival and thus he'd need Maxime and Meredith now that the metaphorical training wheels were off.
Of course that's just my own theory and there are lots of other potential explanations, but the implication seems so clear to me that I'm surprised none of the characters addressed it themselves. The MC somehow learned he could use Maxime and Meredith's worship to sustain Julia instead, so he must have had some sort of off-screen discussions on the topic (probably with Lilith's vision, but maybe with Ruby, Astofiel, or Asmodeus). I wish we had seen more of those discussions first hand rather than skipping over them.
I think the goal of the contest are pretty clear. The House will choose people to appear to in dreams and each time they enter it, they'll know then and only then who the House has chosen this time and the given scenario and have to adapt. We are told that prestations are ranked by how much the dreamer is willing to sacrifice to participate in the dream, so it's clear that demons are ranked at least in part based on how much energy they can extract in a given timeframe with the most efficient being rewarded with a place in the Hall of Fame. It's supported mechanically as well as our "demon energy" indicator from the previous game has been converted into a score indicator that now judges how well we've done in a given scene. The intro also tells us that we can't "lose" during the tutorial mission indicating that they may be penalties if we don't reach a certain score (though that may just be about filling the caution bar).
That seems like a plausible explanation, but I don't recall it being laid out that clearly in game. Even if I missed it, it still leaves the most fundamental questions unanswered.
For example, what exactly is the MC looking to get out of this whole arrangement? The game opens with Domina (a new character) saying we need to reach her at the 'heart' of the House of Hearts to save Lilith. Later on, the MC says saving Julia is his top priority, but she's not the same character as Lilith. Ruby and Asmodeus say we need Lilith's blood to save Julia, so I assume the MC is trying to help Asmodeus free Lilith so he can get her blood, but that's still vague. How does Lilith's blood help, and how does he expect to get it even if he can reach her? Lilith is very powerful, after all, and she didn't seem interested in Julia's survival when she set about creating Julia in the first place. Is Asmodeus going to help with this, or is she just interested in freeing Lilith and that's it? I feel like these are really important topics that the MC must have considered, but for some reason we never saw any of that.
Meanwhile, what about the MC himself? We're told he needs to gain power, but I don't see the mechanics to allow that. I can't believe Helena would specifically negotiate a clause to shield her thoughts from the MC yet allow herself to become his worshipper, so I'm skeptical he can gain power the same we we saw in the last game. But if not that way, then how? Asmodeus says she'll supply the MC's essentials, but does that include demonic energy? Does the MC get a portion of whatever the dreamer sacrifices to see the dream, and if so is that a one time boost or a permanent 'residual?' And what about if Karly gets involved? She's a demon herself, so I'd expect she needs to gain something for her participation. Would that come out of the MC's share or is she just going to be a sort of guest start while being on her own Hall of Fame track?
Basically I don't feel like I understand the setting this time around. The first game did a good job establishing the world (and the MC's place in it) and laying out some short- and long-term goals. The end of that game flipped the table and scrambled those goals - which is fine! - but then it skipped over setting new ones. The MC seems to have picked a new game plan, but I am at a loss trying to follow it.