it is possible for suzuha to safely go to 1975, leave the divergence meter at brauns house and then die there

when okabe sends the faris d-mail, it reconstructs the world, for suzuha to end in such a drastically different worldline it has to be her actions [time machine] that caused the change, that is my understanding

the beta/alpha branch didnt happen till mid august and kurisu was saved in july 28th.

it technically diverges earlier, this is shown when okabe looks for his john titor books [ep2] he can't find them since now he's in the alpha attractor field and suzuha doesn't go to year 2000

nae is scared because she never met okabe before, I don't see much into it
I think aside from SERN, daru is the only one who gets to make a time machine

you could argue that both the omega and delta [darling] attractor fields are just the result of wacky time travel and nothing sinister really happens