decide what period/year you will be portraying and what army.
then what region, western , trans-mississippi, or eastern.
that will narrow it down a bit to your choices.
western armies, federal early war: 1842 smoothbore musket, lorenz european musket, 1841 mississippi rifles, caplock conversions from state miliita armories.
confederate western armies, same as above with some flinlocks & grandpap's squirrel gun & even a few shotguns.
some ohio units carried 1842 till just before the closing battles. though not accepted in main stream re-enacting the two band musket was used extensively in the western region. also enfields eventually both sides.
pretty much ditto for the east till early 1862. then a general issue of 1853 and 1858 enfields for the south with a mixture of 1842, & 1861 springfields from battle field pick /up & state militias & southern clones rifles.
the north imported about 250-300K enfields during the early war but pretty much standardized to the 1861 model springfield mid war.
trans mississippi the forgotten war...used about any firearm they could get.
this is just a general guide line to help you along & inspire you to investigate ...& if you already knew all this then,....good luck with your hobby!
p.s. this just covers the most popular rank & file infantry weapons.