I’m a few days late posting here but what VKC said here is better advice than everything else said (in my opinion).
Don’t try to awaken one or two mythics right from the start. You’re investing too many gems in too little, leaving too much to chance (4x 0.75%) and if you regret your choice of mythic later then you’ve wasted a lot of precious gems.
What I recommend is finding out which mythics are strong AND good in second form. Make a list of those ones then hatch a single copy of them, only when they’re featured alongside a legendary that is also high tier and that you believe would be useful if you got it. After you’ve built a collection of 5-10 second form mythics that are strong and hopefully 5-10 strong legendaries you can begin saving for awakening particular mythics.
Writing this inspired me to go update the guide I’ve got written for all this. I highly recommend going to give it a read. I added extra sections, updated it for the current situation of the game and made it much better and clearer: