>

The real beneficiary is Finno-Swedish relations, as well as NATO as a whole. Going ahead on your own, as well as this whole game of division played by Erdogan, is antithetical to a defensive pact.
Hint: July is after the elections in Turkey.
A good guess to think things might change by July.
I believe Finland already suggested last week to let the talks pause for a while. >

I'm a Finn and I think this is definitely a wise choice. Personally I have no faith in Erdogan saying something else today or tomorrow anyway so it's better to just wait for his tantrum to end and join with our neighbors to the west. >

Is there any benefit for anyone from Finland not joining first?
Attacking Sweden without going through Finland isn't impossible, but it's a lot harder than the other way around. I could see why Finland may want Sweden to wait, but no reason why Sweden wouldn't tell Finland to go first.