On the Horton fairings I see no reason not to keep them, except for possible regulatory issues that others in this forum may address later. Specifically, when one installs the Horton kit, does a Form 337 need to be filed? (My guess is NO, because we install STC items all the time, without a Form.) If a Form is needed and was not filed, can you do it now when only part of the kit was installed? Even if a Form is not needed, is the STC for the whole kit or does it also apply independently to each element -- in short, is it legal to install just these fairings. Going out on a limb, I will tell you that if it was my aircraft I wouldn't care. I know it's safe, no one is likely to notice, and I can always remove them later if someone notices.
On the upper and lower rudder tips you might find a prior message on that, and it's always better for you to do a Search on your items before posting an inquiry, because a) it saves you time by giving you an instant answer and b) you get multiple opinions from readers who have already addressed the topic, and some of those readers may no longer be on this forum. Anyhow, if you do a Google search you will find a company that makes these tips out of fiberglass for many airplanes, including ours, but I found that Don Nieser at Commodore (405-503-4686 or 722-4079,
nieser.02.337parts@juno.com) had new surplus units for less. Since you're sort of new here and will be looking for parts, you may find useful a page on Purchasing Parts on my "backup" Skymaster website at
www.SkymasterUS.com.
Ernie