Does the SQL database depend on how big of the hosting you get? As if your forum (in my case, vBulletin) is like 10 MB and your DB would get the rest of the space?
You might need to explain a bit more...but guessing what you're asking - yes you need hosted space to include the size of the software (vBulletin) and then allow provision for the amount of data your forum posts take up, any space you have available after software instalation will be available to store data. Hope that helps? bg
Yes to your question. Everything in your account including the sum total of all mailboxes count against your total space. But some of the budget hosts also add a restriction on the maximum amount of your space that can be used by the DB. This restriction is there in the tiny type of their TOS. A couple of the big names do this also.