can acting member appointments be used to establish a quorum at any SC meeting?
No
does the use of acting member appointments need to be approved by those present at each meeting?
Yes. Section 34 says “with the consent of the committee …”
To reverse engineer this, if the committee is inquorate, then they can’t vote to allow the acting members to be part of the committee. If the acting members haven’t been approved then they can’t be considered as part of the quorum.
A committee of nine will always need at least five members to turn up, regardless of how many putative “acting members” there might be awaiting approval.