If I have like 10 tabs that use delimiter fields and images in all 10 tabs how does that affect the user account?
Custom HTML fields have no per-user storage. They're just a field object displayed to each user equally and on display are passed through substitutions to allow for unique output per-user, but the storage remains as a single field object row.
I think the account is set to default storage?
Is it possible to set the storage capacity by user group
I've no idea what you mean by this, sorry.
Will the user account just message the user when the account has used to much memory and not allow any upload?
If the user has i frames in the tabs does that affect the performance of the account?
Yes, the more you add to the page the slower it will become as the more complex the DOM becomes. iframes are notoriously awful performance and I don't recommend using them unless you absolutely have to.