Yes, PP is only for i140 to get result in 2 weeks. Therafter u have to wait for i485 result per normal processing. If finance is not a concern do premium processing. The reason i said no need to do PP is since average processing time of i140 is less than i485, by the time ur i485 result comes out, ur i140 result will have already come out. As i said earlier, it's not like they will wait for i140 approval to start processing i485, both will be processed separately n concurrently.

Btw, getting EAD does not cancel h1b. H1b is cancelled only if EAD is used ( only if u update ur h1b info witb EAD info in i-9 employment form in ur office, which is not required) A person in h1 does not need to use EAD. Since EAD/AP can be applied for free if filed along with i485, having EAD/AP can be a backup for any unforseen circumstances but may never be used.