So by now we know that:
1) If five is a higher number, Three or two would be less likely to change.
All other things being equal, yes Lower? Three or two would be more likely to change
As above2) Any lower number than 5 would not allow you to present the puzzle statement - at least, as given
Also correct3) The fact that the word "there" has 5 letters is a very relevant line of thinking
No - this in itself is not relevant, but exploring in this vein could be worthwhile...4) The 5 have a relevant characteristic
CorrectThe fact that the word "there" has 5 letters is a very relevant line of thinking --> meaning that the word "there" has relevantly 5 letters?
no That there is another word that has relevantly 5 letters?
also noThe 5 have a relevant characteristic --> relevant roman numbers
no (f IV e)? Font relevant? (italic?)
no Codes for fonts?
no font size?
no (e.g. there is size 5, while the "are there", written in italic are 3 or 2?) Other technical characteristic?
not in this vein, no Images/pictures relevant?
noIs the fact that "there" is " three" with exchanged letters?
I'm one of the world's greatest fans of anagrams, but this is not relevant to the solution Looking at the puzzle statement "There are five. Are there three or two?", I have noticed that (maybe just for grammatical reasons: the second is a question while the first one is a sentence) the first sentence is specular to the second question: first "there", then "are" and then number, while the second displays first "are" then "there" then the numbers. Is this relevant?
No 
Is it a case where the answer is literally contained in the question?
yes! Displayed in the question?
but no!