What features should be include in a Site Template for selling on Themeforest?
Depends on the subcategory… just look into some items and see what is the status quo. Really there is no minimum set of features, everything is relative to recently posted themes – so measuring yourself against 4y old item is bad idea, also keep in mind that just submitting bare minimum in terms of content and design will probably not make you any sales!
On more practical note there are 2 issues here:
1) passing themeforest quality check – if you have any experience, creativity and talent – better put them inside the zip file your are uploading! Add some gradients, texture, nice photos and good demo content to really showcase various aspects of the design – themes/templates are not like direct customer work where you decide on one matching path and cut the rest – here there must be some room for customization, some options, some additions from which the buyer will choose what meets his needs.
2) meeting the expectation of buyers (aka the actual paying customers) – best way is to put yourself in buyers place: say you are working on Nonprofit Site Template, think and ask questions: who are my buyers? what they want to accomplish using this template? how my design can help them? If I was tasked with setting up a charity page what would I expect and need from the template? homepage with good action call – oh yes, about – of course, some article/blog yes, services – not really, gallery – maybe, something else? maybe a testimony and some social integration to spread the news? what else? if you lack ideas look at some real life pages of that type, try to understand the needs of this customer group better.