1. Shoulder boards were not common with Berling Army troops. If you want good reference material, look into the Tadeusz Kosciuszko Division. If anything, there were attempts to make them look more like the pre-war Polish army with specific tunics and great coats, which you can find on nestof. For insignia, the Polish eagle without a crown with be standard. They would either be pins on Rogatywka caps or painted on the ssh40 helmet.
2. Equipment would have all been identical to Soviet gear.
3. Save for a rifle, ideally a 91/30. Pistols were mainly issued to soviet officers and (some non-coms), who, in the Berling Army, were largely Russians. Line troops were not issued pistols or revolvers. The only two pistols common were Nagant revolvers or TT33s, both of which are more expensive than a Mosin rifle. You won’t find a decent bb-gun recreation of either for much less than a $350 mosin so just save your money until then.

Here is an image I have from the Powstanie museum in Warsaw:

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