In as much as galaxy and star planetary system size distributions
are different, are two different formation temperatures required
within the concept of Jeans' length?

The Jeans length is important for star formation, but the stuff which
forms (rocky) planets is only a small fraction of a larger cloud which
collapsed (as described by Jeans) to form a star. There doesn't seem to
be a lower limit on the size of "planets". There is an obvious upper
limit for (gaseous) planets---stars. The sizes of planets are
determined more by accretion, where gravitation is only one factor.