You’re also entitled to a 60 days visa exemption, and both a tourist visa and a visa exemption needs to be extended with additional 30 days at your local immigration and both give 90 days in total.
You can do another land border bounce. The restrictions of two is lifted, but personally I would have chosen to use a professional land border transport company if you’ve already done several this year.
I guess you mean a 60 days visa exemption. An onward ticket within 60 days is formally required for visa exemptions. Rarely checked at the immigration, but you might risk your airline will request it upon check in. You can alternatively call them and ask for their policy regarding this.
If you plan to stay for six months on your METV you by one ticket to Thailand and one ticket back to Italy after six months.
Then you got one inbound and one outbound ticket.
Within this six months you buy one ticket out of Thailand as an example to Phnom Penh in Cambodia and one return ticket back from Phnom Penh Cambodia to Thailand.
Then you’ve got two inbound and two outbound tickets. Period!
You know your METV gives you 60 days upon entry which can be extended with additional 30 days, so you’ve got 60 or 90 days for your first stay and your outbound ticket to Cambodia.