Mission San Xavier del Bac, Saguaro National Park (East and West), Tumacacori National Monument (near Tubac), Madera Canyon, Sabino Canyon. Lots and lots of photographic opportunities.
What species of cactus? I live in Tucson (this time of year) and am about 6 miles from Saguaro National Park. I suggest that you wander into the desert during the golden hour and see what captures your imagination. Lots of species are blooming now; however, some only bloom at night. A bit of advice: Wear long pants and sturdy shoes with dense soles. Watch where you step (we have lots of poisonous snakes and other nasty critters). And... keep your distance from the Teddy Bear Cholla!
I use a 5DM3 and have a Promaster Digital HGX variable ND filter for those times when I am hiking or otherwise roaming around and want to carry a minimal amount of gear. I've used it with my 16-35mm f/4L, my 100-400mm f/4-5.6L, and my "go-to" lens: 24-105mm f/4L without any noticeable drop in sharpness. Having said that, I also have a set of 3 LEE graduated ND filters (which requires an adapter and filter holder) that I use when I'm staying put in one place for a while). The filter set is more cumbersome, but gives me some flexibility (e.g., desert landscape images with a large contrast between ground and sky) that I can't get with a round ND filter. My advice: Decide how you would likely use an ND filter and then choose accordingly. You can always add to your collection later as your needs change.
If you are doing critical work with heavy equipment, you might consider a tripod and ball head from Really Right Stuff. Definitely not cheap (my setup was ~$1,600 USD), but it is rock-solid and can support much more weight than my heaviest gear. If I'm doing any extensive hiking to a site, I take a smaller and lighter tripod along.
I had LASIK surgery 13 years ago to correct myopia (nearsightedness). Distance vision is still good, but I've had reading glasses since the operation. My ophalmologist is also an amateur photographer and we were recently discussing glasses for computer use (including editing photos). He suggested that a difference of 0.5 diopters is needed to see the computer screen well at the distance most of us use. Since my reading lenses are +1.75, my editing glasses are +1.25 diopters. Hope that helps.