How huge? The maximum GEDCOM which can uploaded to WikiTree is 5000 individuals. However, many of us think that a file of 100 or less individuals, especially for a first upload, is better. There is no way to split a GEDCOM file which you obtain from Ancestry.com. A third-party genealogy program will have to be used to achieve that.
When I first joined WikiTree, I uploaded a GEDCOM. I abandoned it soon as I did not find the process or results satisfying or helpful. I have uploaded GEDCOMs since then, more to refresh my memory about the process than to actually use and to see if I still felt the same way about it. I still prefer to add my profiles manually.