How much are those new APUs projected to cost? Also, is there any information on planned specs?

Not much reliable info, just rumors and speculations. I hope for 6 and 8 core APUs with Navi iGPU in range $150-200.

One other question:
* What advantages do higher-end motherboards have over lower-end ones?

SLI/Crossfire Support, Heatsinking and better VRM's, better RAM memory support, more PCIe lanes, more SATA and USB ports among other things.

For most users B Boards such as B450 is enough if your main interest is gaming.

Firmware fallback/flashing firmware from USB 2 without CPU or anything needed in it is one feature.
Better network chip is another that's often overlooked.
Better heat spreading on motherboard parts that need it.
And more SATA [channels if you need them].
USB count and quality.

I don't go high-end, but I usually go upper-mid for things like this. (Example: My current mobo [bought in September] sadly loses 2 SATA ports when I use the NVMe slot.

Maybe I'm confused, but your first post says you want intergrated graphics, but then you say you want to match current console performance? That's not possible, as far as I know. Running something like Control, even at console settings, would be pretty impossible unless integrated graphics have leaped and soared forward since I last read about them.

this is my current desktop system which came in under a grand Aus
https://valid.x86.fr/bwbkzl

for Linux it doesn't really mater imo so cover the basics, good chip, lots of ram and a Gpu [can be swapped out]

Re-reading my previous posts I think was too messy and not clear, the Ryzen 3400G is a good part but for the same price, there's the Rizen 2700 with more than 2x performance!

3400G 4c8t and based on 2gen Ryzen, can also be argued that is a adapted high-end laptop part. <- 150$ on Newegg
Ryzen 2700 8c16t, no integrated graphics and same generation as the 3400G <- 150$ on Newegg
Ryzen 2600 6c12t, same as 2700 but with fewer cores <- 120$ on Newegg
Ryzen 3600 6c12t new generation, almost as fast as the 2700 in rendering/compiling and the best CPU on the market, except high-end stuff <-195$ on Newegg

The amount of cpu potential power "lost" by choosing a CPU with integrated graphics is enourmous, there are no good price/efficiency/performance cpu's on the market with integrated graphics.

i3 9100f 79$ (no graphics) vs i3 9100 129$
i5 9400f 167$ (no graphics) vs i5 9400 219$

This means that isn't worth buying a CPU with integrated graphics. However The only low-end AMD GPU is the Rx550, wich is very overpriced, virtually the same price as the Rx570 (wich has 3x the power!).
Should you eventually decide to go nVidia, there is the Gt1030 gddr5 wich is a good, cheap and very low power consumption card, can be had in my country for 70 Euros.

All in all, the best "bang for the buck" computer is based on Ryzen 2600, 2700 or 3600. No way around it.(it's so good i'm buying one myself next week).

If anyone are a bit suspicious about AMD stuff at the moment, they are ok. The only use case I can remember, where Intel seem to do sligtly better is high-end emulation. But even those emulators typically benefit from having more than 4 cores.

One issue is power consumption wich can be 20-30 higher (even on idle, typing and watch movies) on higher end stuff. due less efficient Vrm design and higher power/ number of chipsets and controllers. Good for overclockers and masterrace, bad for 24/7 work pc's.
Heck, the new x570 chipset needs a freaking fan cooler!

There are some Linux compatibility issues on some higher-end boards, due the "special" chipsets and controllers used.

Re. VMs and emulation (Dolphin, etc.) in general, my gut tells me to recommend an Intel processor; CCX latency was a common problem with some emulators, particululary the RPCS3. IMO, Intel still has better single core performance.

There is also the TSX instruction set for Intel processors which can be VERY helpful in emulation; I'm not sure whether AMD has developed anything comparable to TSX yet.

You should be aware that at least until recently some people have had problems with AMD APUs on linux with frequent freezes (e.g., when using Ryzen 2400G).

In general, using the most recent hardware will require a very fresh kernel, which can be tricky with some linux distributions, and hardware may not be properly supported for some time. I would do at least basic research on specialized forums about possible pitfalls with linux before making a final decision (this applies to any hardware from any producer, of course).

I would never buy an intel for a desktop and personally I am quite happy with my system which I assembled last year (Ryzen 2600/X470/RX 580), although a couple of modern games still run with glitches on it.

If you want to use rr, you need Intel CPU for the time being. https://rr-project.org/

It is stated twice in this thread why Nvidia is not a good candidate for Linux (also, see the big Linus showing his finger) and explicitly will not be chosen.

120 only for 2600? Here it's about 155... O_o
245 for 3600, and 215 for 2700

Much better than what's offered here, but still, the 75 is steep for only a few more fps up to 3600. If you're going that high anyway the 2700 would be better. Even though single-core is passê and thus belongs to the past, the 2700 is much better for crunching data and background rendering, while the 3600 is better in games. But is the 3600 really worth it?

But then again, this isn't the usual gaming/graphics build.

The cinebench score of the 3600 is a little higher than the 2700 itself. It also feels "snappier" to use, like web browsing... Not only gaming. Yeah, the 3600 is that good!
But agree with you, 75€ is steep for a 150€ cpu and that money is probably better spent on a better GPU or more RAM depending on the work.

For good and updated prices check Caseking.de. We have a couple of nice and updated websites in my country, one of them is their partners.

Edit: Found a nice review of the 3600 wich also includes the 2700 with a lot of number crunching and dev stuff... (not that it matters to the original question itself)
Just for fun, check the gaming performance :D

Hmmm that alone will heavily limit you to pretty much to one of the newest motherboards and processors...

Most CPU's stopped progressing about 2.8Ghz because the amount of heat to dissipate as they went higher was close to what the shuttle engines were outputting (or so i read).

Why not go for eight core 3Ghz instead? Though it would still need decent heat management. And that cancels out nearly all hardware that's less than 2 years old since drivers of hardware tend to be 2-4 years behind...

Wish you luck.