You can pretty easily clear 2nd difficulty with nothing but the two "common" bugs and one or two basic skills in addition to their racial skill. Clearing it unlocks the shortcut for free.This one is fairly slower than the other games but still enjoyable if you don't try to rush things, in the end it's to enjoy your slow life in the island, but that's the grind.
I haven't really done much with the bug fights, at most beaten the first difficulty and Marisa tier 2 but since your bugs "die" in a few days and it's fairly expensive to raise them with sugar water or worse, sap, I pretty much ignored the feature.
I went right away to the extra rinnel and then extra stamps since they increase your allowance and it seems also what you get when you help someone. Also never missing the night jobs since not sure if it's fixed but I get almost double the gold (130 right now vs 70 daytime ones).
For the yubis...umo? -ame? idk, the thumb game, I had no clue what was going on cuz it won't state the rules and it tosses you into the game right away with no pause. I somehow kept winning all the time though lol. Then I figured out that you have to guess how many thumbs in total are going to be raised, counting yours. You can press either button left or right or both. Of course, if you don't feel like waiting 4 days and you really need some piece of furniture and don't have enough money for it, just save and try again Same for the lottery and of course, always bring Marisa for the extra luck.
The minigame at the NE in the forest can be played up to 13:00 but if you are good at it it can be a nice source of affection and either thing you wanted, like 5 lottery tickets if you get the 2nd prize or x10 the price of the piece of furniture you get if you already got it. It costs 250 gold but it pays off.
And even though it's good sometimes that the time moves forward when you move maps while you are waiting it also can be annoying when you are rushing somewhere and just moving there takes over 30 mins and you miss some event. And not a fan that it takes 200 rinnel to unlock the shortcut. Not really many later on but at first it's way too much.
The slow thing is real, several hours in and still haven't unlocked the 3rd girl. Sad that you can't get more but at least they got some scenes.
After Chapter 3 begins you can unlock the buff that increases your BP refund when releasing a bug that's dying to 30%, and that's the point where maintaining your bugs becomes mostly self-sustaining unless you want to push bond with sugar water to go for higher difficulties. You get 27 bond a day for your main roster from one petting and three difficulty two fights, plus 90 rinnel of income from winning. If you do that at least 4 days out of the ~7ish days that your bugs are in fighting condition, you'll recoup more than 50BP, enough to boost your replacement bug to +2 stat growth upon catching. If you add in one or two of the difficulty 1 fights and take the Power Petting 2 buff to increase petting to 10 bond, you can easily boost every bug you decide to take as a main fighter to 100 right off the bat and just steamroll difficulty 2 on pure stats alone even with crap skills.