1. 10b "just as one day in a month is considered a month, one month is considered a year. Ramban mentions this in Kiddush Hachodesh 1:2. Also, there is din miktzas hayom kikulo, like in last day of aveilus, but not miktzas hachodesh kikulo, by aveilus 12 chodesh. Shach explicitly says this.
2. 11a Machlokes R' Elazar and Rabi Yehoshua, whether world created in Nissan or Toshrei - with fruit on trees or buds on trees, is almost - not exactly - similar to what was created first, the chicken or the egg; in a state of potential, or state of actual; (ready to pick fruit). Though animals may have all been created as animals but notice Gemara points out it's Nissan, time for them to mate. The mating process was purpose of creation, which is development of the embryo then fetus.
3. Rashi s.v. Lavshu. See 8a above.
4. Tosfos s.v. Berosh Hashana. 10 makos in 10 months. See this post. This seems to be like Rashi that each maka lasted a month.