I think our dear Good Samaritan is having hard time trying to figure out which adult webhosting plan he should buy. That is not an easy job, if you ask me! Thousands of offers are available on the net and they all seem to be promising but, unfortunately, there is no guarantee!
A reliable Dedicated Server (or VPS) Hosting that is required for adult sites--which consume huge bandwidth--is quite expensive (sometimes up to $700 or so per month). Shared hosting (as low as $3.5 per month) is far cheaper, of course, but it is not intended for a huge site like forumophilia.
So, you can imagine our Good Samaritan with a calculator in his hand while he's awake and also in his dreams!
Now, because I own 2 different servers and several forums myself (non of them are adult ones) and I also setup and maintain all my sites and forums, completely on my own, I daresay I know where the problem lies. If I were in our dear Good Samaritan's place I would first try software solutions (update the current one, optimize the databases, impose more strict rules on anything that is likely to put an overload on the server, etc., or change the software altogether) and leave the server as my last resort.
More important is that you can't have your cake and eat it! That is, you can't have a huge free forum and still expect it to be running without "504 gateway time-out", or any of the 5xx errors, every now and then.