Need help switching (12VDC @ 6amps) and (110VAC @ 17.27 Amps)

The first question to ask is if you can use "low-side" ground switching, or if you need "high-side" +15V switching? You can do the former with a garden-variety logic-level power MOSFET, which you'll no doubt get lots of advice about, but for the latter, you may need to provide short-circuit load-fault protection. You can use a high-side power-switch IC - there are many to choose from. I like the Infineon PROFET series, such as the 40V 38-milliohm BTS432, in a convenient 5-pin TO-220 case, at DigiKey, $5.50

For this you should use a standard SSR module, these run from a 5V logic-level input, are optically isolated, and use triacs, optimally with an ac zero-crossing switching feature. When you wire up one of these, it's a good idea to add a fuse in series with the ac line.

For number 1, as Winfield noted, it depends on whether you can use high or low side switching. Alternatively, you can use a charge pump to get high side switching. If you can only use low side switching, I particularly like the IRF7425 (rated at -12A continuous at 70C, 4.5V Vgs, with an astounding 8.2 milliohm Rds at this drive - astounding for a P-channel, anyway).

I concur on using a standard SSR (Vishay has lots of them) for the AC requirement.

Cheers

PeteS