BirdSpirit. I made a mistake. You cant enhance card that has the same name together. Regarding whether you should enhance on first stage or second. The best is enhance at first stage. Max it and evolve and max enhance again and evolve.
Obviously, BirdSpirit. That a higher stage will have higher stats gain. But in the end is the total that counts. So its best to max enhance and when you evolve you can retain 10 of its stats.
And for MuckGuppy. I have not seen anyone maxing the skill level yet. Currently i can assure you that it can reach level 6. Its the highest i seen so far.