Although both side walls and the front plate are easily removable, the motherboard tray is only removable (from the side) after removing a screw or two.

Cool, so it is different then from most of the Lian-Li cases that I have seen. I should work then.

Although both side walls and the front plate are easily removable, the motherboard tray is only removable (from the side) after removing a screw or two.

No, I don't think so. You can never have too many fans, assuming they don't bother you with their noise. That's why I would advise you to also invest in a baybus of some sort. I'll use the Vantec Nexus now as an example, but there are a lot of others too. I personally use the Zalman Fanmate that is also on that link. (but that's because my water cooled system doesn't need as many fans. Only one on the radiator really, the other on is to cool the disks, the inside of the case and to keep the airflow continuous and fresh)
This will allow you to run your fans at 5v instead of 12v, having them slow down considerably, getting rid al all the noise they create BUT still having them cool adequately. You can control them via the buttons. (except when using the fanmate of course, those are inside the case) Then if you're playing a CPU intensive game and your PC could do with the extra cooling : no problem : turn all the fans up. You're not likely to be bothered with the extra noise your PC will make if you're playing a game anyway.

If your PC has room in the front for two 80mm, then you should be able to mod that to one 120mm (or indeed, at least to a 92mm). Which Lian-Li case it is ? Do you have a link of it on their page somewhere ? It might be easier for me to tell you what I think if I can see what I'm talking about.

Don't relie on your PSU to remove a lot of heat from your case. It already has a lot of heat to remove from it's own electronics. I will help of course, but nowhere near as much as a dedicated fan.
I would still also use that blowhole fan. And I would try to fit a 120mm fan. (blowhole fans are VERY effective since that is where most if the hot air in your case floats to) If it didn't fit I would make it fit, using a Dremel tool. I know it's a hard choice to put a Dremel tool to such a beautiful (and expensive) case. But if you're careful you'll have very clean results, and the added cooling is really worth it IMO.