Blood products are donated in Canada. I got a chocolate cookie. But
since they called me in, unexpectedly, I also ate a very good goat
curry three hours before.

But yes, one must answer a lot of questions.

I have more questions, here. Probably I can guess but I'd like to know:

One donates a pint.

Is this a lot?

Does this lowered volume of blood make it easier on my heart, and
harder on my head?

Does donating blood affect cholesterol at all?

Would this apply too with plasma?

However briefly...

Well, according to the consent form, there's a minute chance of
disastrous effects.  I'm willing to take that chance in order to
contribute to a society in which there will be safe blood and blood
products for everyone who needs them.  Besides, it's far more likely
that I'll have disastrous effects from a traffic accident on my way
there, especially since I walk or bicycle in downtown Toronto.  It's
safer on the subway, but then I put myself at greater risk of
cardiovascular problems if I don't get the exercise from commuting
under my own power.  There are always trade offs.

I don't think there are any personal medical benefits from plasma
donation.  When I donate platelets they weigh me and take my pulse and
blood pressure, which is good to monitor for someone our age.  They also
test the blood for evidence of certain infectious diseases and various
parameters related to general health and blood quality, so I suppose
you might get early warning of some problems that way, or at least have
a lot of baseline data if you do get sick with something later.  But if
you're already donating whole blood every 56 days, you're getting a lot
more monitoring than healthy people need.  IIRC, the newest consent
form states that they may give physical exams occasionally to frequent
plasma donors.

You seem to have a number of misgivings about plasma donation.  You
don't have to do it -- you're doing more than most people by donating
whole blood.  Nobody there will pressure you, nor reassure you more than
mildly:  they want you to be entirely a volunteer.  So think about it,
but put off your decision until you can feel comfortable about it.

Btw, in something like 40 or 50 platelet donations over 25 years I've
never had any but the mildest side effects, i.e. a little tingling in
the lips from the anticoagulant (citrate, IIRC), getting a bit cold
from having my blood run through a refrigerator for an hour and a half
-- no problem, they'll give you a blanket, and the cold is actually
kind of nice in hot weather, and feeling kind of stiff when I get up
after staying in one position for an hour and a half, easily cured by
a good stretch.  AFAIK, plasmapheresis takes less time so you'll have
less of the last two, but you probably won't get to watch a feature
film like platelet donors do in Toronto!