Get 3.4 from VERC also.
You need to install 3.4 first, then follow the instructions that come with 3.5 on how to achieve installation.
two of the brushes are over lapping. unfortunately halflife cant deal when two brushes exist in the same place.You can have two brushes in the same place/overlapping. It's not recommended, though, as it looks really stupid.
it'd probably be a good idea to keep it for map-testing purposes as it's a lot quicker and easier.I'd think otherwise.