So real quick my first question is that my character is trying to craft a lightsaber but he isn't using any of the listed crystals he's using a red synthetic crystal he got from a dark jedi (don't ask), what stats would or should i be using for it when i finally roll well enough to build it?

Second question is what kinda stats do you think Ezra's lightsaber would have?

I would just use the standard Ilum crystal which, unmodified, yields the "basic lightsaber" from the weapon list.

In both cases, I'd just go with the default Ilum crystal, especially for Ezra's since he got his at a Jedi temple.

That said, if you don't want the synthetic crystal to be quite as good as a proper Ilum crystal, you could use the Athiss Cave Crystals from the back of the "Lost Knowledge" adventure as a stand-in, especially if your PC has been awarded less than 150 XP from their adventuring.

I'll probably just go with the basic illuim stats, I can't see Synthetic crystals making a weaker blade than a standard crystal otherwise the sith wouldn't use them

Illum seems to be the standard baseline since it's both in the standard lightsaber and in the upgunned saber from the previous cores.