Follow up questions:
1. You will need power, HDMI, and other cabling to the projector. Is there a problem getting this cabling where the projector needs to go?
2. In regards to screen size, the projector you purchase will have a range that it must be in to hit that size. For a 120" diagonal, for example, the projector LENS may be required to be between 10' and 12.5' from the screen. If your intent is to have the projector lens 23' from the screen, then that projector won't work, and you may not find any projector which will work.
3. Having a decent screen is important. I would recommend one at some point.
4. You have said it is a dedicated room, but by that do you mean you are building the room as a home theater? Or, it is part of a multipurpose room in the basement?
5. When describing the room, please go into more detail: 25'x20' (or so) how high are the ceilings? What color is the paint? What color is the carpet?
6. I want you to consider your local movie theater - what color are the walls there? The ceiling? The carpet? If you want best results, consider painting the walls and ceiling, and consider dark carpet if it is not in place.
7. Anyone in any home can turn out the lights - are the lights in your space dimmable? Are they zoned so certain lights can be off completely, while others are on/dimmed?
8. How 'dedicated' is this room and how dark can you make it and how good of an image do you want?
9. Understand that the cheaper projectors are very good right now, and a dark painted room will look good with them, but better projectors like the JVC RS46 ($3,000ish) will look a good deal better than the Optoma HD25 or the BenQ W1070 at about $1,000. But, if the room is lighter colored (white/light tan/etc.) then the benefits of a better projector may be lost due to room quality.
10. Screen size is typically determined by your seating distance (10') and your viewing preference in a theater. Center of movie theater seating typically has the screen being .66x the viewing distance in width. So, if you sit at 12' then you would have a screen that is 8' wide for 'center of theater' feel. But, if you like sitting a bit closer in the theater, like 1/3 of the way back, then going a bit larger is certainly acceptable. That is, instead of a 8' wide screen from 12' away, you could go with a 9' wide screen or even a 10' wide screen from 12' away... or larger. This is VERY much personal preference, but I recommend people start with THX recommendations of .66x viewing distance for screen width as a baseline. Most people like it a bit larger than THX center of theater feel, so a 8' wide screen (110" diagonal 16:9 screen) from a 10' viewing distance is what I would likely recommend.
11. If walls are currently white, then consider buying a projector first, then running a few movies on the wall at various screen sizes to determine which size you like the most.
12. I'm assuming that you don't know anything about RBE (the rainbow effect) which can be caused by DLP projectors. It may be worth trying to find a store or some place which has a projection setup with a DLP projector to see if you, or anyone in your family, has RBE issues. Please Google 'DLP rainbow' to find more information.
13. Don't forget to buy a ceiling mount. A great ceiling mount is about $150-$200, but you can get lucky on eBay at times. Chief Elite universal mount.
Good to hear you won't have any audio issues. It would be VERY unusual for any contractor to put a screen in place, but possible that there is a space where a screen should go. Measure carefully if that is the case.
Photos or drawings of the room and space that you may be able to provide are certainly helpful. Include your speaker locations, etc.
The Denon you listed is a decent entry level model. Please take a look at Accessories4Less.com for some solid reconditioned models for very good pricing. You may find you want more inputs/power than what the Denon E300 offers...
In a dedicated room, painted dark, I would get a really solid projector like the JVC RS46. In a multipurpose room, painted a light color, I would go with the BenQ W1070 or the Optoma HD25 depending on how they fit my room.