A worthy competitor of the SG, as good as most Epiphone -- & by this I mean REAL Epis, with proper set necks, not the low-rent boltnecks.
Replacing a nut? I recommend you bring it to a shop & pay $40-$70 to have it done. But, if that's not how it's gonna play, then go to any shop (or online)& buy a pre-slotted Gibson-size nut. Plastic is fine ($5 or less) but everyone's into Tusq & Nubone & the like.
Look up a few YouTube videos on nut replacement.
All you got to do then is remove the old nut, without damaging the wood, & leave the slot totally clean & square. The nut has likely been glued in, so you'll need to soften that by holding a heat gun on it for ten or twenty minutes, until the nut practically falls off.
Check to see how the new nut fits, carefully sanding its thickness down until it settles right in.Then check it for proper string height, & again sand it bit-by-bit, keeping the bottom perfectly flat, until the strings are at the height that best suits your string choice & playing style.
The saddle? Do you mean the entire bridge assembly? This is pretty standard for midrange import guitars nowadays. Check Allparts for starters.