There are no limits but the PDF might be unusable if there are 250 pages and many fields on each page. You haven't supplied nearly enough information to discuss server settings. You're better off running a proof of concept and testing your server under realistic and then unrealistically heavy loads to see what happens.
If you do run into form performance problems, one interesting approach I've seen is to remove field bindings and populate the fields from the data dom with scripting. This is a lot of work up front but if your form is performing poorly and a gigantic form is an absolute requirement you may have to do something like this.