Your solo tent should add about 5 degrees of warmth (or, by blocking the wind, eliminate the Real Feel factor.) WM bags are usually rated about 5 degrees conservative, so the bag is probably a 25 degree bag in reality.

Wear dry, midweight or heavyweight long underwear tops and bottoms to sleep in; add a fleece or down jacket and pants if necessary. Also, wear heavier, dry socks and a stocking cap and balaclava (face mask) to sleep in. Make sure the socks aren't tight, since that will constrict blood flow to your feet and make you feel colder. I sometimes carry a separate pair of fleece or heavy wool socks for sleeping, and change out of my hiking socks. You can always add your raingear if it gets colder than anticipated; it holds more heat than you might expect. Just be sure you're not wearing so much clothing that you start to compress the down in the bag from the inside.

Put your empty pack under your lower legs, to extend your sleeping pad to full-length. The thick foam backpad of the Nimbus Ozone will keep your legs warmer. The Prolite Plus pad should be OK at 20 degrees; I've used one at that temperature before. However, if you're concerned, you might add a thin closed-cell foam pad under it.

If you're using a fire, and can arrange an "ideal" campsite, you'll have a large boulder or cliff reflecting heat back toward your tent, meaning that the little micro-climate you're in will be a couple of degrees warmer. Just remember: tents are flammable (spectacularly so; I saw one flare up at a Scout camporee once), so you'll want to be back from the fire a good bit - of course, the further back you are, the less heat reaches you.

Will you be camping at a fixed base, or near your car? If so, some of the extra stuff, like the second pad, can be left in the car for use if needed. Better to have a bit extra in the car that you don't use, than come up short.

I've been fine in Ohio at 15 degrees in January (ground frozen) using a Prolite Plus pad inside a Hubba tent, sleeping in midweight longjohns, balaclava, heavy socks, and a light down hoodless sweater in a WM Megalite bag. Unless you sleep really cold, or let yourself get overly tired, don't eat or drink, or get wet, you'll probably be OK.