Upgrade NetWeaver portal 7.4

Hi gurus,

We are planning to do upgrade EP 7.4 or 7.31

I checked ECC EHP7 (base on NW 7.4) can’t communicate with lower version (under NW 7.3).

We are using ECC 7.01 (EHP4) with portal 7.0, can I do
upgrade portal 7.4 with ECC EHP4?

If we want 7.4, we have to upgrade ECC EHP6 or EHP7?

Please give your advice.