you are more than welcome, it is an interesting topic for me.
as for seeing how chinese was pronounced i believe it would be very difficult to know for sure as the writing system of chinese does not indicate pronunciation. i believe it would not be an easy task to know how chinese was pronounced 1500-2000 years ago, but it would be an easier task to see how the written language had evolved including grammar thanks to a lot of documents.
Ainu language is often regarded as a language isolate, which means it does not fit in with any language groups. it is also a moribund language, no longer used in the community and not learnt by children. it has had some resent interest by younger people who had started to learn but it is a highly endangered language. what connection it has to japanese would only exist thanks to language contact and transfer. genetic studies show that the ainu were long isolated from japanese, i assume they are referring to much earlier times, and their language developed individually.
you are now stating that japanese is a language isolate but previously you were saying is is in the altaic language group so i did a bit looking around because i don't remember reading that in the past. it seems there is no consensus that it is part of this group. it is sometimes included but it a subject of debate by many. the same goes with Korean, which is even stated to be an isolate language like the Ainu language by linguists. as for the Ainu language it is occasionally added to the altaic group. so given this information i think trying to find a link of a japanese word to an altaic language could be even more fruitless than searching within the Chinese language.
this site which is full of information is a nice one to look at for language groups and information about languages. they put japanese into it's own group consisting of 12 languages:
Ethnologue report for Altaic
Ethnologue report for Japanese
my point of this post being that you shouldn't concentrate your time looking within altaic langauges, especially when there is much debate on whether japanese belongs in this group.
we can debate about the origins of a language forever, haha. but yeah i just hope that from this you will look outside the altaic group and look towards nearby languages that may have influenced vocabulary in Japanese.