Well, here's what I know off the top of my head. In a local installation, EG 4.1 and SAS 9.2 work perfectly fine together. I have that configuration running currently on my laptop, in fact, I don't have SAS 9.1.3 installed locally anymore. In an environment with a server, the main issue is that with SAS 9.2 you must have a 9.2 metadata repository to run an EG client-server setup. So, to support your client-server environment, when you upgrade to 9.2 on your server you'll need to ensure you have a metadata repository. SAS 9.1.3 let you do things a couple different ways in regards to the EG client-server stuff -- SAS 9.2 is metadata repository only (no more EG repositories).
I can't find the documentation now, but I'm 95% sure you are correct that you'll then need EG 4.2 to talk to your SAS 9.2 metadata server. Check with tech support if you want to know for sure:
http://support.sas.com/techsup/contact/
In terms of migrating projects, will there be problems? It depends. If you really weren't using any of the server features other than running SAS code, the issues will probably be small. In other words, if you opened data through "Local Computer" and didn't do anything BI-related in your projects, very little will change. Where you'd need to be careful is if:
1. Tables in the project reference 9.1.3 metadata
2. Data was access through a library defined on the server, rather than through "Local Computer"
3. There are BI-related features within your projects, like stored processes
You might need to do some trouble-shooting in the above cases to make sure everything is working in your EG 4.2 environment. Note that you can migrate projects manually by simply opening 4.1 projects in EG 4.2 one-by-one, or there's also a Migration Wizard with EG 4.2 that can make similar changes across many projects at once.
**Shameless plug**
SAS Education (where I work) just finished an EG administration class. Chapter 5 from that class is all about migration, primarily from EG 4.1 to 4.2. The first public offering of the EG Admin class will be through Live Web from June 14-18. FYI, we suspect all the seats for this will fill so you might want to sign up early if you're interested.
https://support.sas.com/edu/schedules.html?id=629&ctry=US There will be other offerings once the Live Web schedule is released for the second part of the year.