Some tips:
-As advised above, use mines to deal with crowds. Specifically, use bear traps to trap a line of enemies, with explosive mines placed beyond them. So when one enemy 'frees' himself from the bear trap, he steps on the mine, which detonates the line / cluster of mines, which kills the line of trapped enemies.
-Bear traps are pretty powerful. They will stop big rats, Siphoners, armoured humans, stuff like that. So don't be afraid to use them liberally. When you get the recipe, all you need is some low-grade steel.
-Put the Cave Ear Poison bear traps in front of other traps. That way, the enemies who step on them will have trouble detecting the subsequent traps. Place the poison traps strategically to give negative status effects to enemies in different ways.
-Acid Traps are pretty silent and very effective, so use those on your stealth assassination missions. Try not to waste them on ordinary luring and destruction of groups.
-Mines are so powerful in groups that you don't need to use the expensive Level III or IV mines in the early to mid-game very much, because enemies hit by the explosions from 2-3 Level II mines should go down. In early game, use the expensive mines to target tougher or armoured enemies.
-Mines are expensive and a pain to drag around. First, get the pack rathound feat as soon as possible. You'll need it in the later game anyway. Next, think in terms of economy and future profits. For example, you can stock up mines to eliminate the Ironheads screen-by-screen, knowing that you'll be able to sell their gear to recoup your costs.
-When you're dealing with whole screens full of enemies that you are trying to eliminate, be a 'ghost' like your build implies. Eliminate isolated enemies silently, without being detected. Then, use mines to eliminate all clustered enemies all at once. Throw a grenade somewhere to get their attention, and when they all come running out, they should all be stepping on mines. They will even mill around because of all the explosions, so any survivors should be stepping on bear traps and such.
-The electrical components on knives make them louder, so it's dangerous to use them for assassinations. Use normal, non-electrical knives to silently remove people when you're on those kind of missions.
-Scout ahead to get oddities in areas that are beyond your level. Your build means that you often don't have to engage enemies until you want to.
-If you are having difficulty with Gorsky's missions in Core City, have you done the missions in Foundry yet? I leave Gorsky's missions until I am ready for the group combat later.
-Going around the tunnels and passages to mug muggers is a great way to dispose of your obsolescent level I and II mines. The fools almost always step on them. Try to silently kill their dogs with bear traps before taking on the main course.
-Start getting used to the toxic gas if you have sufficient chemical skill. It's relatively silent, and could be useful for your build later on.