The only file modification I personally recommend is one to group the templates together the same way your vB
templates are. Personally, I would also add the modification to add the gallery to your forum's admin cp (though this isn't necessary with vB
3.5). Both of those modifications are listed in the readme file, but neither are necessary if you don't want to add them.
As for the database, the only vB
table that is altered is the language table to add fields for the phrases, which most vB
hacks are going to do if they use the phrase system. Other than that, things are inserted into the tables for the templates, phrases, cron, etc, but no other tables are altered.