Help me to get the right mini split! 24.000 BTU enough?

I need a mini split for keeping the temps in my rooms right. Is for the following setting 24.000 BTUs enough? I used the sticky ventilation thread as a basis for calculation, but I am not sure if I need to calculate the ballasts extra, and I didn't calculate the pumps and fans in.

I have two sealed rooms (flower and motherplants), total 16.7 x 12.2 x 8.5 feet (1731 cubicfeet) (5.10m x 3.70m x 2.6m) which are side by side and have between air circulation by a big fan and ducting.

The stuff I need an AC for:

4x 600/750 Watt double ended HID
1x 200 to 400 HID light for vegetation
1x 750 watt dehumidifier
1x water cooled propane co2 generator (I could place the water reservoir outside of the room)
1 x 100 Watt clone light
some small pumps and fans

So in total around 4250 Watts (maybe a little bit extra for some pumps and fans) if running flowerlights at 750 Watts. Mostly I will run them at 600Watts. That would be 600Watts less and result in total 3650Watts.

Good would it be, if the unit can heat also.

How many tons should I get? I did read that it is better to split the load on two small units, but I don't think I will do that.

I need the unit to be quiet, because it is not common here to have ACs. It will be behind the building at a wall which is you can't see from the walking paths. Are stronger units louder or more silent?

When is an unit too big? Can you get it too big?

How reliable are the different brands?

I did that there are units where you don't need an HVAC guy because the lines are preloaded or whatever. Is this usually the case? Probably will need to do it myself.

If you want something really quiet look at a Mitsubishi mr slim I’m sure there are others that are quiet too . Mitsubishi is one of the well known ones around here ! But you will need a tech to install it unless you own the proper tools and know how .

Heat exchanger.ca located in BC , Canada sells ready to install AC units with charged lines.
Are both rooms 16.7x12 ?

Bigger unit more noise . A bigger unit will just short cycle . It is best to match it close but have some wiggle room , with 24,000btu you have some wiggle room IMO

18,000 btu could be enough

ok. the proprietary doesn't allow anything to be installed outside. But I could do inside something. But somehow this might get a bit tricky. I was thinking about a custom solution. Actually I was thinking to put a outside condenser unit of a mini split system into an insulated box inside the building and ventilate this box with outside air.
Here in detail my approach:
This insulated box would have two fans, which are each matched with the cfm rating of the condenser unit and pull air into and out of the box (from and to outside of the building).
I was looking at some of the mini splits and it seems that you can find outside units from mitsubishi which move around 2000 cfm.
I was thinking about using two fans (ruck etamaster 355 Ruck 3320m³/h) which are each able to move around 2000 cfm.
Each fan uses at maximum load around 250 Watts of power. Considering a mini split has a COP rating of over 1, I think that even with the extra energy use of the fans I would come cheaper (energy wise) than anything else what would be possible in my place.
Can I build in another room an insulated box which contains the condenser unit and this box is connected to ducting which inputs air (from outside of building) and ducting which outputs air (also to outside of the building)? I know that the condenser needs big amounts of air, so I would install two fans which are each able to move around 2000 cfm of air. I would install one fan for pulling air from outside, pushing the air into the box and then another one pulling the air out of the box and pushing them outside. The fans were chosen under the assumption that most mitsubishi condenser units (in the range of power that I need) are able to move around 2000 cfm max each.
If I could use such a design, I would need to add 500 Watts total for the two fans. I think like that I would still be more energy efficient than other solutions. Maybe only one fan would also be sufficient, then I would only need 250 Watts extra. I am only able to use some indoor solutions and unfortunately geothermal pumps or swamp cooler are not possible. I know it is a bit problematic to find such device if you need a 2 to 3 ton unit.
So what do you know, would such a setup work? I have not enough knowledge and experience in HVAC, that is why I need to ask a pro.
So far I have some concerns:

• Are the outdoor condenser units working with variable fan speeds, and is it a problem if my inline fans blow directly onto the condenser unit? Maybe the airstream of the inline fans, messes with the heating or cooling process of the condenser unit. Also has fast moving air some sort of own effect in temperature (e.g. cooling through windchill)? If it would be the case that direct air has some detrimental effect on efficiency of the unit, I probably could use some sort of wind baffle like it is offered by Mitsubishi (https://www.pinterest.de/pin/469500329886926899). What do you think?
• I live in a climate where in winter we can get temperatures as cold as -5 Fahrenheit. It happens rarely but it can happen. That situation means that I would need a unit which would work also in these kind of temperatures. Mitsubishi offers Hyper Heating units which work in these temperature ranges. Unfortunately it seems that the Mitsubishi 2 to 3 ton units which support Hyper Heating are almost only twin systems (have two fans), which would mean a combined airflow of 3600cfm. To provide 3600cfm of air with my inline fans to the insulated box where the condenser unit would be in, I would need to buy much stronger and much more expensive inline fans. So I only know the Mitsubishi units so far, but maybe somebody of you know the product range of the other quality brands. Does somebody know a unit which is capable to work in low temperature settings and has a cfm rating of around 2000cfm? Other option would be if somebody knows strong inline or other fans which would be able to do 3600cfm and are actually not that expensive.
• also what do you think, would I need two or one of these inline fans? I mean suffice how much would such a condenser unit have postive influence on the static pressure. Would the outdoor unit be a resistance or an noticeable aid in pulling air for one fan in such a setup?

So that is the situation. Maybe somebody can answer some of my questions. Thank you very much!

If water consumption isn't an issue or you have access to a large enough reservoir water cooled AC would be a good option that would not have any components mounted outside and outside ambient temperature has no effect on them.