Upgrading doubt

Hi Experts

We are upgrading sap hcm from Ecc 5.0 to Ecc 6.0.

We also upgrading portal from EP 6.0 to EP 7.0.

We have 5 customized PCRs in previous verson.

I have some doubts

1) Do i need to take any precautions before doing upgrade ? If Yes What are they ?

2) Does this upgrade have any impact on my PCRs? If yes what kind of impact for example: in tables or PDF document etc?

3) is there any other input regarding both upgrades ?

please help

Regards