Should a company be referred to as “he/she” or as “it”?

It or they.

Google buys more of our servers than any other company. They have bought 4,000 servers from us.

Well, you definitely don’t want to use he, since there is no single male antecedent, nor she for similar reasons.

The notation he/she is severely unappealing for a whole multitude of reasons, but beyond its ugliness, it still won’t work here because there is no single notional individual behind it all.

That leaves you with they or it, either of which is fine. I don’t think a native speaker would bat an eye at either of those two. The difference is subtle, and not worth making a big deal over.

I believe I would be more likely to use they than I would to use it in this circumstance, but I’m not positive. You’d have to catch me doing it when I weren’t thinking about the whole idea, then see what I actually did. Saying it over and over again in my mind has robbed it of any natural spontaneity, and I’m no longer sure what I’d do in practice.

'It/they' are totally okay. However, 'she' is also recommended considering organization/agencies, just as human beings, countries and vehicles, are also productive, hold lives of employees and give forth career growth opportunities etc. Use it! 'He' is not appropriate though - even countries are hardly ever referred to as 'he' unless in French vocabulary