With that design, you're hitting 110dB SPL at listening position with 120 watts. Always halve the power output from your amp, to ensure you have headroom. 6dB is sufficient in most cases, though for subwoofers I'd like 10dB, just in case (listen to James Taylor's 'Gaia' to see what a bass transient can do to your system - it bottoms out every single woofer and subwoofer I've ever heard...
It looks OK. You will be able to work with that combination. Doubling the power adds another 3dB and I'd really like that additional grunt in my room, but you'll be fine too, as long as you don't go overboard on the levels and overload the amp. And the sub will not bottom out even with the 500 watt amp, the driver is at just about its limits with 400 watts, and will survive 800 watt peaks (two-way excursion).
Remember the recommended amps for this driver are all in the 400-1000 watt range, and if you don't need that much grunt you may as well drop down to the RS315HF and the SA240 (or BASH300, my preference). The SA240 is a great partner for the RS270HF/HO, and if that driver works in your room I would suggest partnering those two. There's not much point driving a Maruti 800 on Michelin Corsas, to take an extreme example, but you could if you wanted to
You won't lose whichever way you go, but I would save my cash and get a more 'appropriate' combination.
Post some pics whenever you're ready.