The best way to con a man is to sell to him his greed...
Think of it this way:
I own the property, I have a R4-6million rand asset. My expenses only come to R30k and I'm pulling in R120k, why would I sell this property when there's a tidy R90k profit I am making MONTHLY.
You've mentioned that you don't know much about the industry, which is the first red flag.
The second red flag is that lease renewals are coming up, so it looks like the owner is trying to cash in at the top end as he/she expects leases to not be renewed or renegotiated at steep discounts.
Third red flag is that you didn't mention anything about getting an independent valuation or getting an inspector to evaluate the property (it could be an unstable structure that may collapse anytime).
There's too many factors you haven't considered or are out of your control. You're also increasing your risk exposure beyond 100% by standing as a joint surety to a bond on the property.
Of course, everything I say may be utter bull and this may be a great deal you have on offer, so the risk is yours.
As far as what to do goes, I would follow the suggestion of rather buying offices for your own company first and letting out to other smaller tenants (if there is space).
Diversifying from technology to real estate could be equivalent to saying that your zip-producing factory would like to diversify into the abbatoir industry (there is no direct relation between the industries, so you're not capitalizing on any known flaws in related industries and you're setting yourself up to get eaten by guys who know that industry).