>>Having good friends is a wonderful thing
"Having good friends" is a subject..although it contains plural word (friends).

Rising costs <OF middleman>......has.

"Rising costs" is a subject of this sentence.

Smoking lots of cigarettes is/are dangerous for health?

please be sure to post the correct answers.
OG11:

The rising of costs of data-processing operations at many financial institutions has created a growing opportunity for independent companies to provide these services more efficiently and at lower cost．
(A) The rising of costs
(B) Rising costs
(C) The rising cost
(D) Because the rising cost
(E) Because of rising costs

OA is C: The rising cost... has...

rising is gerund used as a noun modifier modifying cost. Rising is not part of the core subject. How can you test this? Take out "rising" and it can still make sense. Main subject is "cost", and main predicate is "has created", so the subj-verb agreement is singular.

For your first example, farooq is right in that "having good friends" the whole phrase acts as the main subject. Here, you cannot takeout "having", so it is actually acting as the main subject