1) What type of bossing do you mean? Shadower wins for best soloing (good shadowers can solo horntail pretty easily). I/L are extremely helpful for Pink Bean and HT limbs/zak arms, and come out as one of the top dpsers against multiple targets at range (as narrow as this sounds, it includes most major bosses: PB, Cht, ht, zak, chzak). Marksmen win for straight up single target dps, but not by a massive amount. Throw in multiple enemies or potion cooldown and the other two come out far ahead. Before I can give a definite answer, I need to know what type of bossing you're looking for.
2) Ice Lightning mage is arguably the ideal class for LHC, especially when you consider CL's massive bounce range. Marksmen excel as unfunded chars since snipe has "set" damage. Shadowers are somewhere in between, and still great choices. I'd suggest (as unbiased as I can be =\) I/L for this area. CL is just too amazing at LHC, and couple it with DoT moves and AoE, and you've got a great mobbing class.
3) Two months ago I would have said I/L arch mage, and it would be incredibly tough to argue against that. However, hackers have dropped the price of PoTs through the floor (as low as 500k in Kradia now), so I'd have to guess Shadower, but only if you can pull off regular HT solos later on. Beyond that, no class really excels at making money. Some can save a bit faster, some can kill a bit faster, but you'll hardly get rich by looting alone.
My personal opinion is obviously going to be biased since Marksman is one of the few 4th jobs I haven't played and my main is an I/L, but I'd lean toward I/L mage with Shadower at a close second. Shadower will be much more expensive, but will end up making quite a bit in real "end-game"