Questions about Day Tours and Planning for February Trip

So many questions! My husband and I are going mid-February to Greece. This is our first time to Greece. We have our hotels booked.
We will not be renting a car so we will be using a tour guide/company or public transit. So far our itinerary is as follows:
1 night Athens (arrival day)
4 nights Nafplio
9 nights Athens
Our plan is to use Athens as a base for most of our trip and do day trips out of the city.
We would prefer to have guided tours of the ancient sites because we feel that we would get a better understanding than if we just read the signs.
We are interested in trips to Delphi and also Meteora (monastaries). If we did Meterora, we would stay overnight for 1 night.
I am worried about the weather for those trips. Specifically if it is icy or snowy.
We do plan to go Aegina for a day trip also.
So the questions:
1. What tour group companies do people recommend for day trips or the Acropolis etc? We could use a private guide but I assume that would be more expensive.
2. How can I find out specifically what the road conditions and weather is like in Meteora and Delphi?
3. Is it possible to book the day trips last minute (Meteora/Delphi) or do they fill up in February?
4. Other day trips out of Athens or towns to visit by public transportation?
5. Day trips or public transit to places outside of Nafplio?
Thanks for any help! We have been to other places in Europe but our first time to Greece.