Lazy bugger get the drill out. . Lol . . . . I've recently done exactly same thing on Router but used Nut bolts didn't tap and didn't take that long really. (My rack was pre drilled thou)

Tig will work but for the little extra work I'd be inclined to Drill.


On another note I noticed in another thread you mentioned no CNC experience. Let me warn you now that Plasma requires that your electrical side is done correctly otherwise you'll have nothing but issues from electrical noise coming from the plasma.
The mechanical side is fairly simple and relatively light weight so don't need massive power or build but the electrical side needs to be Rock solid.