Space Calculation and retention policy

hi guys

I have this scenario right now I have 29 VMs around 3.5 TB storage used. All are Thin provisioned.

I have to implement a retention policy like this:

Weekly backup on Saturdays and this Weekly backup will be retained for 4 weeks each.

Also the last  backup at the month has to be preserved for 6 months.

So I was thinking something like this

0 Daily

4 Weekly

6 Monthly

OK my question is there a way to figure out/calculate how much space I am going to need in 6 months?

will be enough 1 VDP appliance 2TB or I am going to need 2 VDP appliances 2TB each to balance backup jobs and achieve this policy retention?

thanks a lot