Can I plug a conventional XLR microphone into a wireless transmitter?
Yes. Although only “plug-on” transmitters are likely to have the option of providing phantom power to condenser mics. “Body pack” type transmitters typically are not designed to provide phantom power although you can buy/make a cable that will connect an XLR mic to most any body-pack transmitter if using a dynamic mic or a self-powered (battery) condenser mic. We don’t know exactly what you have in mind by “table mic”, but I am assuming it is something with an XLR output.
Can I use two transmitters with one receiver?
No. Although there are some DUAL-receivers that actually have two receivers inside the same case.
Can I use transmitter and receiver from different product brands?
In some very rare cases this might work, although probably not optimally. But in virtually all cases, you must stick not only with the same brand, but the same model if you want proper operation. It isn’t a matter of the same frequency bands or even the same channels. Different brands use different techniques for processing the audio to improve performance.
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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.