microcams question

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I don’t see umbrellaing as a big factor in the decision of choosing a Z4 over a Totem. Personally I double up Z4s and Totems in the .2 to .75 range, primarily because of the size difference. Any given Z4 will be slightly smaller than its Totem counterpart, with the difference becoming less important as you move up the sizes. The Z4s are bomber in placements where black to purple Totems are just slightly too big to fit into the crack. 

Get the Z4s in the 0.3-0.75 size at least, I use Z4s in that size and a black totem and don't find myself often using anything else. Can't speak for quality of sizes below black totem as I never place them (or rather, haven't yet).

I would just get another Totem. Umbrellaing is not even remotely on my list of concerns but that sweet sweet Totem crag cred definitely is. 

Another vote for the Z4! As others have pointed out, they're just slightly smaller at each size and it can be really nice to have the diversity in size. The .3 to .75 Z4's are a great complement to the totems.

Rack of totems black to green and rack of Z4's 0.3 to 0.75 compliment each other really well and are more versatile than "standard" cams (C4, Friends, Dragons) in the same range. For a double rack in 0.75 and under especially, I'd take bendy narrow head cams any day. That said, I love the New Friends with extendable slings for straighter climbs, no need to add an extra draw, so I happily rack those when the going gets splitter. 

I would get one of each. Like mentioned above they are slightly different sizes and compliment each other well. Sometimes one fits better than the other. 

Another vote for one of each. Sheds some grams and gives you more options. 

Totems + Z4 doubles is my go to setup. 

I find the double axle Z4's to be super fast and easy to place and clean. I highly recommend those four sizes (0.3 - 0.75). Everything about the Z4's is low profile and ultralight, that offsets the bulk and weight of totems in my pack. It's hard to beat the Z4's ability to slot in like nuts, making for extra confidence inspiring placements. Totems excel at this too, but the extra range, stiffer stems, and cam stops of the Z4 are slight advantages when complex slotting is required. It's hard to beat the holding power of Totems and their ability to deal with funky placements. 

All modern cams work well and do the job. The Z4's and Totems just make things easier. For me they are the ideal combo. 

Potential downsides: 

The sizes pretty much match from 0.3 to 0.75 (Z4's are a hair smaller) some people like their doubles to fit slightly different sizes. IMO, the range of these cams nullifies the need for "off sizes". 

If you are mainly climbing sandstone maybe it is better to have doubles with wider heads and thicker lobes? 

Totems are also heavier and bulkier than Z4's as others have mentioned, so for long approaches, alpine climbing, etc I tend to bring the Z4's, they are basically the same weight as the C4 ultralights but feel more versatile. Plus if I did have to bail and leave a cam, I wouldn't hesitate to use a Z4 but I would die a little if I had to leave a totem.

II'll echo the comment about placing Z4's first if it's an easy placement and saving the totems for funky ones. But honestly if you have the cash for a double rack of totems and you love totems then that keeps things pretty simple having all the same gear.

Cam-parison chart