Input appreciated please.
There are lots of really dodgy "switch your XXX mains appliance from your YYY uC" circuits and schematics out there. Many of them dangerous. A lot of videos do this stuff on breadboard

I am trying to design a "breakout module" that does this "properly" and safely. It may/will ultimately need to come in a proper physical case, properly isolated, protected & appropriately fused etc so that people can do these things without killing themselves or the equipment.
The concept has 2 parts:
1. The HV switching part
2. a slave uC which you can talk to via I2C, analog, or whatever
I am focused on part 1 here.
Attached is an early sketch of the basic switching architecture. Text annotations are the questions I would like input on.... Also see more verbose description of goals/intentions and circuit operation below.
Many thanks
EDIT:
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My original circuit description and outline of intention/goals were not adequate and caused some confusion below. So here is a fuller description:
I am not making a simple SSR, nor am I making an AC motor drive. Variable speed AC drives (VSDs) have a full rectification stage first then a DC bus with huge caps and then an H-Bridge type switch topology. The advantage of that is that they can make AC of any frequency, and this is required to properly control the speed of AC induction motors. My circuit can't do that, but it can operate in the following three "switching modes":
1. ON / OFF multi cycle period (typically 1-2 seconds, less and, depending on load size, you get into trouble with standards in some regions,( eg EN61000-3-3, AKA "the flicker standard"). The uP can (optionally) do the careful timing to ensure it switches the MOSFETs off during zero cross and hence causes less harmonics. This mode does the job of an SSR - if this is all I wanted I should use an SSR - and is quite trivial.
2. What is often referred to as chopping / dimming / phase angle switching etc. Means turning the devices on / off once per 50/60Hz half-cycle. This can be done on the leading edge, ie wait after zero cross before switching on, or on the trailing edge, ie turn the devices off early before the half cycle completes. The former (ie leading edge) is what triac based dimmers do, but they can't do trailing edge which has advantages in many circumstances.
3. PWM of the sine wave at frequencies of multiple kilohertz. This is different to the AC variable speed motor drive because it is not switching DC to make AC of any frequency. It is switching the AC sine wave. That means we can "smoothly vary the effective amplitude" of the sine wave, but we cannot change its frequency. -- Note that while the attached circuit sketch can do this in theory, in practice, a proper isolated MOSFET gate driver is needed for this mode, as discussed below.
So proper induction motor control is beyond the scope of this "research break out board". It's purpose is to introduce hobbyists / students to the various kinds of AC switching you can do. It should be able to demonstrate the above 3 modes, and how different kinds of loads respond to them. The purpose is to educate and provide information on strengths weaknesses, from a "ready made box" which can do all 3 modes and be SAFE. Someone below mentioned current/voltage monitoring and that would be a great addition. Non-trivial due to the isolation requirements, but I might need to go there.
Some notes on intended circuit operation:
Unlike in a VSD H-bridge, the 2 MOSFETs will always "switch on at the same time".
Actually that is not quite correct. more precisely, in the "upper half cycle" (when Vline > Vneutral the lower MOSFET on my schematic (Q2) will be in "body diode bypass", ie whatever you send to its gate is irrelevant. In that upper half cycle the "triggering which is important is on Q1. In the lower half cycle, the roles are reversed. --
EDIT2: The above paragraph is wrong (I learned something), the body diode is not used like that. Both MOSFETS are really on together in that circuit, because MOSFETS can conduct current in REVERSE (ie from source to drain) when they are on. The Ron of a MOSFET will usually result in a lower forward voltage at a particular current than the body diode, so if it's switched on, almost all the current will flow through the main channel, not the body diode, and that's good => lower power dissipation.
The optocoupler & +12V supply referenced to joined sources and that pull down resistor mean that the controller/uP doesn't have to care which half cycle it is in. It would just look at the zero cross info from U1 and decide when to trigger U2 - upper or lower half cycle, don't care.
Discussion below introduces a proper isolated MOSFET driver which fundamentally works in a similar way but drives the devices more efficiently and therefore able to achieve Mode3 = PWM > 1kHz.
It is also possible that IGBTs would be a better choice of switching device, particularly for mode 3. Any input on this appreciated. -- EDIT2 discussed below: No. IGBTs are not good for this, because they can't conduct in reverse, and hence need a separate anti-parallel diode (there is such a thing as a RC-IGBT, reverse conducting, but this is not a mature technology).