Is it worth switching from retired “one” plan?

I’m with t-mobile since 2013 and during the years being adding lines to my account with various promotions. Currently I have 8 lines paying $210 total with autopay and I’m still on retired plan “one”.

Is there a real benefit switching to a new t-mobile plan Go5G or it’s essentially the same?

If I switch, will I keep my price with all my promos?

also for 100GB premium data that comes with Go5G plan, is it per line or it’s per account for all lines?

Thanks