If you really can't get a job with AMR Boulder (Denver is a different animal), Northglenn ambulance, Poudre, Platte, Thompson Valley, Denver Health, or any hospital then Rural/Metro is pretty much the only place left to get your feet wet. I'd pick Rural/Metro over any of the smaller ambulance companies that operate in Denver.
I'll elaborate a little on the points Chaz and Tigger hit.
Yes you will start on a wheelchair van, this is pretty typical of most agencies that have a wheelchair van. You will get a few days orientation on the van, the down side is that you will be with another wheelchair driver, who is likely also extremely new and may be as lost as you are. Tigger points out that you are supposed to progress from there to BLS and then to ALS and then potentially 911, however this isn't always (or usually) the case. Some employees only spend a few days "clearing" for BLS which largely involves sitting in the back of a Pridemark ambulance in Wheat Ridge and taking vitals if you get a call. If you are lucky you will end up in Aurora doing the same thing (you are only lucky because the FTO's are nicer in Aurora). From there you may work a BLS shift, or they will throw you with a medic at their convenience. If you get put with a nice medic they might be able to catch you up to speed with what you really need to know on an ALS ambulance, or you get stuck with an a**hole who may just yell at you and roll their eyes if you don't know how to do something. I've heard that the second is more of the norm than the first. Getting on a 911 ambulance is quite a stretch, many people that are currently there really don't leave very often just because the 911 ambulances don't get worked over like the GT (transfer) ones do. You might end up in Aurora if you are lucky after a year or so there, Wheat Ridge is seemingly random when they decide they need to clear an EMT.
As far as Aurora goes, Chaz pretty much nails it. I will say that as an EMT it's actually a pretty sweet system. You get to run emergent, start IV's, thump on chests, and generally see some sick people. You may even get to attend on some pretty sick people since AFD and R/M might miss it completely. Working as a paramedic there is generally pretty frustrating, if you disagree with AFD you can actually get fired for speaking up. This results in a lot of people just keeping quiet. Some crews will let you run calls or make decisions if they really know you, but this is heavily dependent on the crews and is pretty rare. One of the other things to keep in mind is that while you will get to see a lot you may also be watching the very wrong way to do things happening.
Overall, as a first job it's not the worst place to work. Just know that if you want to move up and move on you will need to go elsewhere.