Yes. The following unit will support 14.3 payload.

Yes. Please be mindful that the following unit has a payload cap of 14.5lbs

You could use this on the main tube...https://www.bhphotovideo.com/c/product/1421986-REG/smallrig_1925_30mm_rod_clamp_for.html/qa

Manfrotto FAST GimBoom Carbon Fiber has a diameter of 48mm.

The base of the Manfrotto FAST GimBoom Carbon Fiber (1/4"-20 and 3/8"-16 Mounting Stud) has a 3/8"-16 mounting thread in it's base, so you could mount the monitor to the base of the boom, but that positioning may not be ideal. Instead you could consider using a Impact Super Clamp with Ratchet Handle (BH #IMCC106R • MFR #CC-106R) to clamp around the boom and act as a mounting point for an articulating arm.

Depends on how you want to use it. A monopod is designed for being upright and on firm ground. if that is how you plan to use it then the Monopod has a very clear advantage (some of them have feet which make them even more stable) If you plan to use it for booming like demonstrated in the photos then Monopods have a couple of disadvantages. 1. They are not designed for being operated like a boom. Normally when you are using a monopod your hand is near the top of the monopod right underneath the bulk of the weight. this reduces the leverage of the payload you are putting on top of the monopod. If you hold the monopod from the far end and raise it in the air (like you would often do with this GimBoom) it may not support the full weight of the set up resulting in bending or even breaking the monopod. 2. Monopods contain unnecessary components. Depending on the monopod you are referring to it may have extra parts that work well for monopods but are detrimental for boom poles. For example its common for monopods to have 3 or 4 sections so that you can compress the tripod down in size more however this is bad for a boom pole. that design reduces the integrity of the boom pole when held from the other end (resulting in bending or breaking). 3. The GimBoom has some features that make it more comfortable to operate such as 2 padded handgrips. Because it is designed to be used as a boom its also reinforced so that you do not have to worry about bending or breaking as much as you would on a monopod. The GimBoom is much closer to a Boom Pole like those used by audio professionals more than Monopods used for video. Its a simple lightweight, sturdy, extendable pole that allows you to get dramatic camera movement using your camera and a gimbal. Monopods technically can work but The GimBoom is designed to be more comfortable to operate, easier to use, and reinforced to ensure that it lasts longer.

Yes, the Manfrotto FAST GimBoom Carbon Fiber (1/4"-20 and 3/8"-16 Mounting Stud) would work with the DJI RS3 Pro gimbal. Please make sure that your payload weight is below 14.3 lb for the gimbal and camera or it could malfunction dropping the entire gimbal payload..

If you want something extremely sturdy I recommend the Manfrotto Virtual Reality Aluminum Base (B&H # MABSECONVRUS MFR # MBASECONVRUS). Also consider the FEISOL TT-15 Mark 2 Mini Carbon Fiber Tabletop Tripod (BH #FETT15M2 • MFR #TT-15 M2)