the point is that Digimon Heroes is an even bigger grindfest with a far more punishing business model if you decide to not grind and yet I see people complain about the super laid back experience Links is so far. But to actualyl answer your questions:
Once you get some friends via discord for example you can take turns in farming for the materials. You don't need stamina to join a coop group and a organized group will always block out randoms so that everybody can join. For example if you and 2 other friends have 60 Stamina that's 9 Hard runs for all 3 of you.
Mobile games using a friendcode system isn't something uncommon and Digimon Heroes does the exact same thing.
Chips drop from PVP and special events.
Each Digimon has a Signature Skill tied directly to it and a legacy skill that can be what ever the F*%§ you want it to be. It's normal in Digimon games especially since this game is Cyber Sleuth Lite.
You can save your progress by using the transfer system, which Digimon Heroes also does.
This games Payment model is suspiciously player friendly actually. Unless PVP Makes the 5 Chip slots super important I don't see the negative here. It's pay to skip which is much fairer than pay to win which most mobile games do.
Version upgrade is basically a +5 for Digimon that are kinda outdated and need an extra boost to be relevant.