Ariats run narrow/small and aren't as good of quality as they used to be (7-8 years ago). I wouldn't recommend them.
I have had great luck with Mountain Horse boots. I prefer the pull on or zip up for ease of use. Blundstones are also very nice. I plan on buying a pair of those for my next pair. Both brands run true to size.
Any suede, leather, or synthetic half chaps are fine. The color should match your boots (black or brown). Measure your calf at the widest point over your jeans or breeches, pulling the measuring tape or string TIGHT. I have Arete chaps and really like them. They have some synthetic chaps on clearance sale. Apparel - Chaps - Arete Equestrian - Half Chaps, Skito & ThinLine Saddle Pads, Browbands... - (Powered by CubeCart) Ebay
is a good place to look too.