The plot WILL eventually pick up, but this is Okayado's first serialized piece of work so i imagine that he's being forced to go for what sells currently, AKA ecchi harem rom-com, and the first tankobon sold amazingly well over the span of just 2 months. The last chapter, as i said, most likely just worked on introducing some side-characters, the series is not even a year old yet. Odds are that over the span of the next year he'll finish up introducing characters/giving them special chapters that focus on them(Like Miia's shedding chapter HNGGGGGGG) the plot, will pick up i imagine. The plot after all is that he has to eventually pick one to marry/couple it up with. Also Okayado is a total bro, he is all about healthy loving relationships, i can't imagine him dragging it on forever with no real progression(It just doesn't fit into what he's been known to make prior to Monster musume), so i'm hoping it picks up soon, but yea, it's a slow start.
I wish it would've just been all about Darling and Miia being lovey dovey, that'd have been the best for me, but i am enjoying it a lot regardless.
Also planning on ordering the two first volumes of Monster musume soon, was surprised after realizing how relatively cheap it'd be to import.
Monster Musume
I just can't see a real plot picking up. I've never once read an ecchi rom-com like Monster Musume that didn't pick up on the plot full time until it got closer to its end. There will be chapters that do progress it somewhat, even chapters that are devoted entirely, assuming it doesn't get the axe soon, but series like it are almost never very heavy in plot.
Also, it's not the mangaka's first serialization. He had a serialization in 2010 that didn't last long, just got to one volume.
It depends on where you order the stuff from. Your options are typically either paying a lot to get it quickly or not paying a lot and waiting weeks to months. Though I suppose it might be a bit different where you live, as you're not in the US. I order the magazines I get off of Amazon JP (for getting them asap) and it costs me around $60 just for 2 magazines. There are cheaper alternatives but the time it takes is a bit much, and as a scanlator, I'm a bit impatient when it comes to new chapters.