Isn't there some convention about which Madhya Laya Bandish can and should follow a particular Vilambit Bandish, considering the

There may not be a definitive answer to this question, as the approach and thoughts vary to a large extent from style to style..

Just trying to share here my thoughts..

The purpose of Hindustani Classical music is primarily to present a Raga, and the Bandish then just becomes a tool in the process. The literary meaning or the expression of the lyric takes a back seat. This naturally reflects in the selection of the Bandishes, which is done purely from a musical perspective.