回复：Question: H1B status when H4 starts working with EAD

Could I still maintain my H1B non-immigrant status, if my wife applies and starts working with her EAD?
yes.

Or I will be required to get an EAD and surrender my H1B?
No

another question, my 6-year H1B will expire in 8 months, should I extend it to the 7th year,
Yes.
or should I start the EAD? what's the advantage/disadvantage to do so?
Keep H1b for in case your 485 will be denied. Then you can have long time to deal with the problem