There's been a few threads recently on starting a forum from an existing site or as an offshoot of another type of site that you can find on the first page of a few different boards here. The unfortunate thing is that gaming forums are a dime a dozen and very hard to get off the ground because they have so much competition. If you have an existing, successful site, however, you may be able to convert your readers into posters.
I am not sure what you specifically mean by causing issues. You may have problems with integration between the profiles of your commentators on blog articles vs the profiles of forum users (your readers are most likely not going to want to have two accounts, so connecting the two will be important).