I’d think about the AP you need carefully. If you’re looking at low density coverage (maybe 10-20 devices with no high bandwidth applications) then you should be able to use the MR74 which is 2x2:2 and then you can use, for instance, an Omni-directional on the 2.4GHz to provide client coverage and a patch antenna on the 5GHz directed to the gateway so as to maximise performance on the backhaul. Or if the repeater and gateways are close enough to you could just use omnis. For the MR84 the 2.4GHz and the 5GHz are on both top and bottom ports, so you should use dual band antennas, and both the antennas should cover the same area (due to the way MRC, MIMO and beam-forming works) this means you need to pay attention to where your clients are (I.e. the client serving coverage) and also how you’re achieving your backhaul connectivity.
Cable wherever you can, that’s always best and just use the Meraki mesh where you get really stuck.
You can workout how many APs you can support on a MS120-8FP relatively easily. Take the PoE budget for the switch (124W), and divide it by the power required for the AP, 21W for the MR84, 11W for the MR74. So it could comfortably support 5x MR84, or 8x MR74 (it ends up being limited by ports).