You may enter for F7 in advance of passing F1, F2 and F3 but any exams from those three that you are not exempt from must be entered and paid for in the same session that you do F7
F3 would be a major help with F7 studies (you don’t make it clear whether or not you are exempt from those first 3 but F3 would be good to work through even though you may be exempt)