I've purchased three new 9mms in the last year and half. I've been using Federal Champion 115 gr FMJ for break-in and practice. I can get a cash & carry, out-the-door price of well under $200.00 a case locally. I would think about using the same weight that you intend to carry for practice and break-in . I like the lighter grain bullets because of the lighter recoil in the polymer frame guns but many will like the heavier, slower bullets for good reasons. You'll probably get a dozen good answers to this. Everyone likes something different. Stick to known brands and avoid the really cheapo stuff ....too dirty and smoky. Lot's of good choices from Remington, Sig, Hornady and Winchester. Clean your new gun well and keep it lubed. I suggest using a good gun grease on the rails and slide for better break-in. Oil tends to "run out" on long surfaces. Have fun, shoot safe. Happy 4th ! "Independence is not a right...it's a reward for hard work and diligence."

You can use virtually any 9mm loading as break in would be similar for any quality 9mm ammo. As a rule of thumb I use a target load that is close in velocity and weight to my preferred self defense load.