What's Medusa? A hero? For Griffins tower it should not be done too soon because some stuff here can be rude if you make it too low level. In theory dodging won't win much more time than killing what's on the path.
There's a good opportunity to make the griffin underground later, sea chest need to be report to harbor close to the Griffins and take all chest won't lead you close to this harbor. So even if you go close to griffins island first, not make it yet is a wise choice and make it only when later you'll report the sea chests quest at harbor. I had the opportunity to do that but instead I did Griffins underground asap so at level 7 and well I got there 2.5 nightmare fights.
One of them was so rude that I lost 7 Cursed Ghost and had in my army not enough Cursed Ghost to restore their stack with fighting, first time it happened to me.
No Mana Spring? Man you are very good if you can do it without this spell.
For Freedom Islands do it in 1/2 day seems a bit extreme. I won't say it's not possible but I think that if this is possible, it's by skipping any fight not on quests roads. If I was you I'd try a quick scouting with cheating to time it. Take care that in this case the time is always faster than with a real play. It's because you do it quick and forget details or even won't quote the army impossible to beat that will make you lost time.
About Vampires and Cursed Ghost:
- You cannot sacrifice any undead (nor plants, stone and units immune to magic).
- About taking the hit, I don't like vamps much I feel them too weak.
- Ghost are too difficult to manage when your army size becomes bigger and when your attack increase.
- Cursed Ghost are extremely good units if you don't aim for zero loss. The 50% physical resistance and ability to regenerate during a fight are priceless.
- Vampire don't have this resistance but Ancient Vampire are rather good despite they don't have this resistance too.
- Cursed Ghost is the perfect target with spell support in 70% of the fights but for many of those fights it's a challenge to succeed keep them on control. And that's possible but take a long time to learn.
If you have ancient vampires I'd suggest you try them to take the hit particularly if you have sacrifice. If you don't have sacrifice or don't have ancient vampire I'd suggest you try cursed ghost and be patient with the unavoidable errors you'll do about controlling them. Take care that they show their best if you can provide them spell support ie Stoneskin and Archmage Shield. But in many cases to control them you'll need use only one of those protection or use it only at first rounds. In tougher fights with target you'll certainly need both quite often. Peacefulness is another option to keep control on them more easily but objectively most often it's not the best option.