Minimum is 2. 4 is where it starts getting strength. 6 is the standard where time and rythym permit. More than 6 is good for emphasis or slow build where desired. Much more than that and it begins to become cumbersomely long, and the anticipation grows maddening as the audience awaits the sweet release of “choo choo.” One chugga, unless used as part of some sort of nihilist or defeatist punchline, is the providence of madmen and the uneducated. I can forgive a single chugga in non English speakers or native speakers who are mentally infirmed as they have valid reason to not be familiar with custom or not sense the fundamental wrongness of the rhythm in regard to the intended purpose of the sound in English phonetics.
Odd numbers just sit wrong on the tongue for such a matter.
(also I have no idea what you are talking about)