Upgrade from NW 7.01 SPS6 to NW 7.3

Hi Guru's

We want to Update ECC6 to EHP5 and Upgrade NW Portal to 7.3.

We are currently on ECC6 EHP4 SPS6 and the NW Portal on NW 7.01 SPS6

We have PPM 4.5 Java apps running on the NW 7.01 Portal.

Question 1) Do we have to upgrade PPM 4.5 to PPM 5.0 or will the JAVA apps run on NW 7.3.

Question 2) Do anyone know how much effort will it be to re-compile older Java Apps. (Before EHP4)

Question 3) Could anyone direct me to a site/document about a functional project plan/steps to Upgrade to NW 7.3.

Have a nice day

Wynand