Huge amount of choice in terms of bodies and lenses out there now, will depend what you mainly are going to use it for.
I wouldn't be looking at an A7RIII at this point, a.f doesn't really keep up with the newer bodies.
A7IV is a good all rounder although I personally absolutely detest the flippy screen and while other rave about it's a.f performance I haven't found it to be that great tbh.
A7III is a good solid shout with a 3k budget you can pick one up used for around £1000, leaving 2k for lenses, flash, cards etc and what ever else you need.
A9 is great for anything that moves fast and is the only one of those you have mentioned that has a usable silent shutter, blackout free shooting is a gamechanger. Being an older body it doesn't have some of the bells and whistles of the A7IV, but can be bought so cheap now used are amazing value for money.
The Sony 24-105 lens is okay for a 24-105 f/4 but its a pretty boring lens.
At the cheaper end of the scale these are all decent:
Sony 35mm f/1.8
Sony 85mm f/1.8
Tamron 17-28mm f/2.8
Tamron 28-75mm f/2.8
Samyang 45mm f/1.8 (if you get a good copy, lots of variation with these)
The best lenses I have had for Sony are:
Sony 50mm f/1.2 GM
Sony 135mm f/1.8 GM
Sony 24-70 f/2.8 GMII
They are all crazy money though and depending on what body you buy might take you out of your 3k budget.
Personally with 3k to spend I would go with an A7III or A9, 35 f/1.8 and an 85 f/1.8. leaving cash left over for all the other bits and bobs you may need.
Used prices would be along this sort of range:
A7III - £900-£1000
A9 - £1200-£1400
35MM f/1.8 - £400 They often pop up on Amazon at this price new
85 f/1.8 - £350
Grey market places like Panamoz and E-infin are worth checking out as can sometimes be cheaper than used. You could prob buy an A7IV, 35 and 85 for the grey market places new for under 3k.
If you need flash Godox is the the most popular choice for Sony, personally I prefer there flashes that have a battery pack included of those the V860III is the best one, they also have a round head flash V1 and a smaller V350s model.
My use may well be very different than yours though.