It's not very hard, especially if you stick to either Windows (not recommended) or use a pre-built OS like ETHOS, which is $39 per rig, which is totally worth it IMO; it IS just a minimal build of Ubuntu geared towards mining, but the $39 is worth not having to build the distro yourself for me. It'd be cheaper to buy the hardware and assemble the rig yourself (by at least $1k most of the time), and you can customize it, so you could start with what you can or are willing to spend now and add onto it later (just as long as you buy a motherboard with enough pcie slots, I recommend at least 6 unless you just want something small). The other nice thing is that as new tech comes out you can upgrade in stages with what you can afford instead of having one huge price tag all at once, but honestly it's really not that much of a difference in price for hardware vs income if you're smart about what you buy...
But if you don't want to/don't have time do that, and are solely focused on ROI and profit, then I suggest the L3+, or the S9 if you're good at wiring, for the garage, or the R4 for inside.
Basically ASICS are the better short term investment, GPU rigs are better long term (and more modifiable obviously). I'm primarily a Mac guy with a little bit of Linux knowledge and it took about a day for me to figure out ETHOS. I currently have two ETHOS rigs (one with 3 Nvidia 1060s/3 1070s, and one with 4 1060s), an S3, and an L3+, and I have some broken S5s I picked up that I've been playing with for fun. I don't prefer ASICS over GPUs or vice versa, though the ASICS are definitely more of a "set it and go" which is great, but less fun to mess with (and far more limited on what you can mine with).
Oh, and I second the "run a line out" if you're planning on putting it in the garage; it won't be a HUGE loss, but you want as strong and direct a signal as possible, as though miners use next to no bandwith, they are constantly sending and receiving data, so any moment of signal loss will cause delays or rejections. Again, overall not much, but if you can run an ethernet line, I would.
thanks so much for all of the information. I think I will just go with the L3.
Someone mentioned to me that they need to be at a room temperature of 72 degrees. Is this true? I havent read this elsewhere. So now I'm concerned about putting them in the garage with no ventilation ??