The Multiplier is designed for 20x20 a FC and a 4/1 ESC, a micro-cam, and an axii-style antenna:
For links and such, see the rotorbuilds page: https://rotorbuilds.com/build/20989
Motors: Anything with M3 19x19 mm mounting holes will work. We prefer 2207-2306-ish stators in 1700-1900kv. My current favorite is the Talon / RCinPower 2207.5 1850kv, or the Hyperlite 2207.5 1922kv
ESC: Any 20x20 4 in 1 ESC should fit. A fair amount of over-size is OK. We use the Aikon/Talon 35a and the Spedix IS40
FC: Same deal, anything with a 20x20 footprint. We prefer the Talon F4V2/F7V2/Fusion.
Camera: The pod was designed with a runcam racer / racer nano in mind, but should fit any micro-sized camera. You may need to make some adjustments for cameras with very wide lenses, but the body should fit fine. I'm currently using the Racer 2, but have a couple Nano Racer 2's inbound.
Rx: XM+, Xfire Nano, etc. Some people (myself included) have had issues with the RXSR in close proximity to the VTx, so i'd advise against it unless you really want that telemetry.
Vtx: AKK Oscar's Backpack, TBS unify nano, or anything with that size footprint. I like to tape my backpack to the back of the camera, but there is also room on top of the stack.
VTX Antenna: Axii - 2 MMCX (or any axii-style antenna with a connector matching your VTx.)
Batteries: 6S 1050-1250mah (or, to tame it down and lose a bunch of weight, try a 4S 1000-1300)
Props: Anything in the 5" family (including 5.1 etc.) will fit. My personal favorites are the HQ 5.1x4.5x3 and the new Headsup R38's
Little Stuff: 20*20 fiberglass top plate, 19 x 250 mm strap, nylon washers/spacers, M3 O-rings, 4 nylon nuts. (TBD I may start including this stuff with the frame, LMK if you have strong feelings about it). Zip ties and heat shrink for Rx antennas.
LEDs: sometimes hard to find for skinny arms. I prefer addressable ones so that I can turn them on/off at the same time as the pit switch on the Vtx. : https://tinysleds.com/products/femto-8-led