I am by no means an expert, but I would say that, yes, after Kamoshida's palace and the celebratory feast at the hotel, the game does start to open up more. However be prepaired for the long haul, each palace works like Kamoshida's - you have a deadline, and have to wait until the end of the deadline to advance the plot - but some palaces will also force you out at a certain point, before reaching the end.
So to have more time for social stats and confidants, you should attempt to finish each palace in one visit, even if it feels like a slug - as long as you have SP to spare, you should continue, it will save a lot of time in the long run.
I don't know the most efficient way to raise your social stats - I guess if you are up for it, you can do some min-maxing by saving before everything you try, to see what gives the most points to a stat. But yes, I agree, they do seem to take forever to raise, especially if you have all but one raised, like "when do I have enough points?!?!?" lol.
I played my playthrough without the DLC's - I didn't know they were free until after I defeated the last boss... - so I do not know their strangths and weaknesses. But whenever possible, you should try to recruit some new Personas in battle, even if you don't plan to keep them, you can reclaim and use them for fusing newer and stronger Personas later on.
The last thing I will mention is the two Confidants I would consider important to max out early - if you plan to attempt an all max confidant playthrough - would be the Temperance and Fortune Teller arcanas, as they both have skills that help cut down on preparation time and other stuff. The Fortune Teller arcana can even give boosts to your Social stat earnings.
Hope this will be helpful, and that you are/will be enjoying the game.
Ps. I should probably mention - in case you don't know - that in order to unlock the Third semester, you will have to max out the Faith, Councilor and Justice Arcanas before a deadline in November