Hi,
I've done this before and it really a complicated process and things can go really messy. To begin with, you know that you won't be able to migrate extension data, but only Magento core stuff like products, attributes, orders, etc.
There is no guarantee the migration will work for you. If someone says they can make it 100%, it's a lie. The tool has lots of imperfections and doesn't know to deal with many situation that are DB related.
It's a long process to even start the migration process, configuring the migration tool needs exceptions of all your db tables and fields that are not recognized by Magento.
If you can understand that and you're able to take a chance on this process to fail, I am willing to give it a try. I succeded 2 times and failed once, because the tool outputed an error that could not be traced.
Lookup my profile and if you think we can work together, reach out and we'll talk more.
Thanks,
Cosmin