PI 7.3 Dual Stack Vs Single Stack

Hi,

My client has R/3 4.7 enterprise version. Although they are going to upgrade ECC 6 in the future, they would like to implement PI 7.3 and run through some interfaces for setup.

I am aware that proxies are not supported due to Web AS is less than 6.40.

I will be picking up some IDOC/RFC based interfaces only currently.

My question is whether they should go for PI7.3 Java stack or dual stack.

1. If i go for JAVA stack only, can i communicate with R/3 4.7 for IDOC and RFC. Is there any limitations for this?

2. Assuming if i go for ABAP and Java stack, is it possible for me to upgrade from 7.3 to 7.3.1 since I heard it is not possible to upgrade from Dual stack to single stack.

Please let me know the same.

Regards

Krish