Personally, with 357 magnum loads using slow powders like Lil'Gun, H110, etc. I'd use the small pistol Magnum primer for more reliable ignition. Some would say it might not be necessary but I think it works better. Most reloading books list magnum primers with "magnum" loads.
I have found the Hornady 158 grain FP/XTP over Lil' Gun to be the most accurate load I have tried in my 1894C. The flat point will also hold together at carbine speeds and provide excellent terminal performance. I use CCI small pistol magnum primers with Lil' Gun.
In my experience the only way you can get away with standard primers and slow powders in the 357 is by using a really heavy crimp. It helps cut down on the spattering of unburned powder granules, though the heavy crimp does cut down case life a whole bunch. I now stick to the mag primers for slow powders.
I use LilGun powder for my .357 revolver and 44mag rifle. It didn't seem to matter if I used a regular primer or mag primer with the .357 load but with the 44mag, the regular primer works best in mine.
I do used mag primers when using the W296/H110 or 4227 powders.
The 158g XTP-FPs are exellent bullets in the 357 rifles. Watch your velocity though if you decide to use them on deer. With Lil' Gun, you can push the XTP-FPs past their limits if you're not carefull.
I've killed quite a few deer with that bullet, and it's quite deadly when you keep it within the right velocity levels. I wouldn't trust it "any" faster than 1800 fps(muzzle) if you might get a close shot on a deer. Even at that velocity you stand a very real chance of over expansion, and poor penetration if you hit a facing shoulder the wrong way. If I was using them(I switched to Remington SPs) I'd keep'em at around 1600-1700 fps. XTP-FPs are great bullets, and very consistant in performance, but when they do reach their limit, they can fail very quickly.
As far as your primer choice, I personally have had the most consistantly accurate results using CCI 550s in all my 357 magnum loads, including my lower powered 125g bullet Unique loads. I also use a firm crimp(not exessive) on every 357 load. I firmly am convinced that a uniform crimp(cases trimmed every loading) is more important to accuracy than anything else.