EDIT: WHHOOOOPS! I see you did share room size, not sure how I missed that - with that size of a room, you are going too small .... upsize.
Original reply:
Without sharing room size, it makes it tough to make a definitive recommendation.
I just went through the same process - upgrading my 10-15 year old home theater, and cycling out my Denon 4806 (which is a wonderful AVR) and Def Tech speakers for something a little more beefy.
My room is 25 x 16 x 8.5 ft ceilings, and I opted for RP280F front, RP-450C center, and TWO R112SW subs. If I was going to purchase just one sub it would have been the R115SW. I plan on upgrading my surrounds to RP-450S soon, and even adding Atmos front height RP-140s to get to 5.2.2. Let me tell you they sound wonderful.
***EDIT - you would need at least 280F, 450C and 15in sub(s) IMHO for your room size, and consider 7.2 with 250S surrounds. That is a great space, do it justice. What I have is a tiny bit of overkill for my space, but would be great in yours. In fact - if I had that size room, I would change one thing - Get the RF7's for the fronts if you like to listen to music in two channel. Otherwise the RP280 is fine... I know, I know, your wallet is screaming in pain right now - but read the bottom of my reply. Deals are out there if you are patient.
I will say the RP's surprised me - I am an old closet audiophile that has been down the "separates" road in past years, but has been relegated to AVR / HT solutions because of time, space and budget.
The Denon 4300H - while not underpowered, this is Denon's Made in China line, and although still technically a "good" receiver, it is not geared as much to music / 2 channel quality as, say the 6300H or 7200W would be IMHO. Even the x5200w, or the x6200w would be a great choice - both now discontinued and deals still to be had on those. The higher end Denons are still made in Japan - and have a little better components, if that matters.
But if you are mostly HT, then the 4300H will serve nicely IMHO. Something to consider - if DTS:X, HDR and 4K are not a big priority, the Onkyo 1030 is on Amazon right now for $999, and the 3030 for $1100. These came out about 1.5 years ago, discontinued in June '16 but are absolute power houses for music and HT. Note these are throw backs and 45 or 48 lbs respectively, but are great if music is a priority. Only bringing it up because they are in that "state" of final inventory being cleared, folks have moved on and they represent great value. Note the WILL do HDCP 2.2, are HDMI 2.0 (not 2.0a) - but the 2.2 is only on one input / output HDMI port. (I just bought the 3030 as I plan on keeping my VT60 plasma for a number of years, plus the 4K dust needs to settle - let others fix the bugs and the standards settle out - I never like to be on the bleeding edge when it comes to HT).
As far as price - consider this - I picked up my two R-112SW's at Fry's for $219 per sub, the RP 280's for $419 a piece and the center channel for $430 - all at Fry's on deals / promos, and all about a month ago. So, "price" is relative, and if you are patient, wait for deals, you can actually do quite well. I am sure that gives a "no way" reaction - but I actually stumbled on the SW price when the sales guy put the promo code in and told me I just saved 230 per sub... that was a good day. I took my wife out to dinner with the savings ;-)
Cheers.