First - do yourself a favor and google Calmini, maybe check their BBB ratings - I will not repeat what I have heard or read, but I will tell you that the last time I bought anything from Calmini was in the late nineties, back then my experience was not as good as it could have been, and that coupled with what can be found on the internet today is enough to keep me from making that mistake a second time.
Moving on - I don't think you need a lift (or spacers) to run 215/75R15 tires, I don't know what the OEM size on the Tracker is, but on a GV, it's 235/60R16 or 215/65R16, which work out to a 27.1" diameter - your 215/75R15 works out to 27.7" so not a large increase and I have a buddy running my old 225/70R16 (28.4") all terrains on his GV with no lift and no issues - if the 225's clear with no lift, then you should be fine with the slightly smaller rubber.
I'm one of the people running OME (on a Grand Vitara), camber is within spec with no camber bolts, so no need for fancy new control arms, and I'd say OME's reputation for ride quality is well deserved - general cornering & handling is superb for a two ton lifted SUV, and I have no regrets going the OME route - my one "complaint" is that OME doesn't make suspension for my Mitsubishi Pajero.
I do have freewheeling front hubs, they are not essential, the vehicle can be flat towed with or without them, so whether you choose to fit them or not is up to you, either way you will need to maintain the existing pneumatic freewheel mechanism in working order or modify the front differential to eliminate it.
Good luck with your build.