Just wondering, do i require an onward ticket out of Thailand if i choose to enter from Cambodia overland and getting a visa exempt after Oct 1st ( 45 days)?

No.

In theory yes, in practice no. Visa exemptions require outbound ticket, visa holders do not. But don't think they ever check. Not even airport immigration does, but airlines often ask for an outbound booking at check-in. 

Just came back from Cambodia nine days ago and was not asked,