What are the requirements for proof of accommodation and flight when entering Thailand on a METV?

Hi guys, my passport just came back from Rome with my METV.

I have Italian passport and I will land in Bangkok on Jan 15th.

To apply for this visa, among other things they required proof of accomodation to cover at least 80% of my first stay.

So... I had planned to book the hotel for the first week and the flight to another country 60 days after the arrival... but I had to buy a flight after 1 month (that I won't use) and book an apartment for the entire first month.

Now I have a couple of questions for you:

When I enter Thailand for the second time (I guess around the end of March), if and when they ask me the 3 proofs...

1 - Will be enough to show the hotel reservation just for a few days, instead of "80% of entire duration"?

2 - Is it ok to book the flight after 90 days, knowing in advance that I would extend my stay for 30 days more? Or to avoid any problem I should book a cheap one within 60 days?

Thank you!