I think one of the problems with HT is there are few places to get a good demo. Audio is just as important as video to get a good HT experience. Placing speakers where they are convenient is not going to give good audio, it will give you sound but hardly quality audio. Good acoustics starts with location, location, location! Location of seating, location of speakers and location of subs. So lets start with some very basics.
1. Seating - Do not place against walls! Moving the seating at least 18" from the wall is going to make a difference. It might not be the best spot but it will be a big improvement. It is too much to discuss now but do not place them in poor modal areas. You can do your own research on that. I realize many are doing media rooms and not dedicated HT rooms. But getting the seats away from wall is big.
2. Speakers - You can also do your own research on where speakers should be placed, Dolby, ITU, THX, etc.. Start with not placing your speakers near corners, the floor or ceiling. If they have to be near walls or surfaces those need to be treated, research SBIR to start. Front speakers at the same height for a good front soundstage and panning, ideally placed at ear height. Well set up speakers will have good clarity, focus, envelopment, dynamics and response. The soundstage should be seamless all around you.
3. Subwoofers - Yes at least two. Bass response in small rooms have a varied response between seats when using one subwoofer. Unless of course you can place that subwoofer somewhere in the middle of the room which is rarely practical and also decreases output significantly. Two or more subs is used maintain seat to seat consistence in the bass response. Again do your research, Harman has some good papers for this.
4. Acoustic Treatments - OK. I understand many people aren't going to this level for their acoustics but if steps 1-3 are done well you can still have a great HT experience.
5. EQ - The final tweak. EQ can not fix room acoustics. Although they call it room correction it really does not correct the room. There is no type of EQ that stops sound from reflecting off the various surfaces of the room. EQ done well is the icing on the cake. EQ done to correct poor acoustic set up is a band aid for a large hemorrhage. In fact studies as well as user experiences show that EQ sometimes makes problems worse. These auto-magic EQ systems can't solve these problems.
If you want to trade off acoustics for a big screen that is fine, but know that it is a big compromise. You trade off dialogue intelligibility, clarity, good imaging, a great soundstage and envelopment with terrific dynamics that can't be achieved if the screen is where we need to place the speakers. If you are going to place you center above the screen you should place your L/R speakers above the screen as well and treat the ceiling. All aimed towards the listening position at least they will all be on the same horizontal plane and you can keep your L/R from being in the corners if your screen takes up the front wall. While not as good as an AT screen it is better than mismatched height between the L/R and center and avoids corner placement. You will get the effect of being spoken to from god but if the seating is not too close it is reasonable compromise for a media room. In ceiling speakers for side surrounds are not as good. There are some specialty ones that can work but most regular ceiling speakers I wouldn't recommend for this application. Some speakers placed high on your side wall slight behind your seating would be much better.
Going back to big screens in general and not just the acoustic compromises of not using an AT screen. There are two other big considerations at this type of size. As stated before one is the pixels get large and you get that effect of looking through a screen door. This is more prevalent with LCD projectors like the 5020 as the pixels have a bigger gap between them making it easier to notice. Other technologies like LCOS and DLP have a smaller gap between the pixels and you can be further back before you notice this effect with them. In fact the JVC with E-shift would be ideal to not notice this effect but is more expensive.
The next is how bright the screen is going to be. The bigger the screen, the dimmer the picture gets. There is a standard to get good 'pop' out of the picture. There is a minimum reference standard for cinema, it is 12 ft/l (foot lamberts) for film and 14ft/l for digital projection in theaters. Many theaters do not achieve this. We try to get al least 12ft/l in the home. If you are going to have ambient light you'll want more. For reference 10-12 ft/l is still pretty good for viewing, not reference but enjoyable, 8-10ft/l is watchable but it is noticeable that it is getting dim. 6-8ft/l watchable in a bat cave and we lived with this for many years in the CRT realm but picture is DIM. So let's look at how this translated to the 5020 and 170" screen. In its best picture quality mode the 5020 puts out ~700 lumens +/- 150 depending on placement. Within the zoom range of the projector there is a 40% difference in brightness between placing the projector at its closest point from the screen compared to its furthest point. But we will use 700 for basic calculations on a 1.0 gain screen. This gives ~8 ft/l, definitely dim especially with a new bulb.
Now the Epson has brighter modes such as living room which has about 1500 lumens and dynamic which has about 1900 lumens mid zoom. So this big of a screen can be used in these modes but you are trading off picture quality. The other thing to consider is bulbs lose 50-65% off their brightness as they age and about 20% in the first few hundred hours then they gradually decrease over their lifetime. I usually recommend people start with at least 20ft/l with a new bulb or if they choose changing their bulbs more frequently to maintain brightness is an option. Also, if this is a media room and you plan to watch with light in the room I'd start with more than 20ft/l, more like 30ft/l+ would be better. It does depend on how much light and where it is placed to determine how much it will affect the picture.
Working in this industry we often hear people say they want the biggest screen they can fit. I like big screens myself but know the limitations and the tradeoffs. Sometimes bigger is not better.