Where to begin--It sounds as though you want a mid grip striker but no other specs or desires have been mentioned. Unless you have a special bolt/port configuration in mind, why build from scratch? If you have the donor rifle already, sell it, whole or in pieces and find a ready built striker. It sounds as though you may not have the donor so that's another expense to bear. I fully understand the thrill of Do-It-Yourself--I have 7 bolt action Savages and only two are still virgin, but not for long.(both are Strikers). You asked about caliber choices--unless you're thinking of mule deer, I would consider .243, .260 or 7-08. As far as recoil is concerned, they all have considerable muzzle jump, but otherwise, its how you hold'em--they are hand cannons! (REALLY FUN hand cannons)

Now, since you live in California, here's my suggestion: Start looking for a used one in California and if possible, buy it. Don't worry about the caliber, you can pick up a take-off barrel on this site and probably sell the original if you're so inclined. California is really your main hangup-I'm not suggesting to not go by the rules, just work with them. After living in CA for 47 years and being a gun nut for 42 of those years, I can tell you alot of horror stories.

There are still alot of questions that you haven't brought up-bench gun, target gun, field gun, optics, stocks, etc, etc. I suggest that you visit and register at Specialtypistols.com. If you would like, PM your phone number and when to call and I will call you and we can discuss some of this stuff.