Dear Janice, (Not necessary if this is an informal letter with a close friend)

I am glad that you seem OK and are well prepared for the Good Samaritan hospital’s alumni event. [... and seem to be well prepared for the upcoming alumni event at the Good Samaritan hospital.]

I check it more often than the other one.

Both are available, although. [Either are fine to use, though.]

Sorry about the late response and I’m really sorry that I myself don’t know their email address that you really want to know. [I'm sorry about the late response and I'm also really sorry that I don't have the email address that you're looking for.]

Here is an idea: the Japanese Boston company has their branches all over Japan.

I’m afraid that it might not be in time for this coming HRS in San Fransisco but you’ll definitely get them in the end and might use them next year.

I believe that Keiko Usui is the perfect person to manage this kind of problem, and I'll let her know.

I hope that I will see you in Boston next year.

Please give my (best) regards to everyone. (We don't usually say "best regards." Usually we just say, "Give my regards to everyone.")

Both are available, however. ("Although" implies a condition that follows. Example: Although we were tired, we still went to the party.)

Sincerely, (Just my opinion, but since you said "best regards" in the previous sentence, it felt a little awkward to me to repeat it as your closing to the letter.)

I do still use both, although.

I’m afraid that it might not be in time for this coming HRS in San Fransisco, but you’ll definitely get them in the end and might be able to use them next year.