If you don't know anything about pedals and shoes, then work with your LBS to get it right. The difference between speedplay and look or shimano is essentially personal choice unless you need a lot of adjustability, then it's a speedplay game. The main thing here is that setting up a pedal system is more important than the changes between the systems and getting properly fit in a shoe is also more important than where you buy the shoe. Done right, it works great. Done wrong, and you can pretty much cause significant pain in any part of your legs, foot or back. The adjustments are subtle but they matter.

Shoes are a huge deal to get right. Most cycling shoes tend to run narrower than other athletic shoes. Road shoes need to be sized to fit closer to your foot and it is not what you have in your street shoes. Pay attention here - shoes that don't fit can be excruciatingly painful and it likely won't be evident in the store where you try them on.

Road vs Mtb systems is basically about walking comfort vs pedal platform size and stability. A road rider tends to pedal in the same position for a longer period of time, hence the cleat/pedal combined platform size is more important because of the repetitive pressure in the same place and in the same way on their feet/legs. An mtb rider varies their position more so there is more tolerance for a smaller platform in a tradeoff between varied position, walking and pedaling. I prefer road pedals given a choice, but on my adventure bike (use on vacations and back roads), I go with mtb pedals. For mtb pedals, it's pretty hard to beat the new speedplay offering (syzr pedals) because of the adjustability in float and because using them does not depend on the tread on the mtb shoe - the shoe is basically out of the equation. I have a pair and really find them to be a major step up for me over the Time ATAC pedals I had which I found to be a major step up over the Shimano SPD cleats I started with on my mtb. For road pedals, speedplay has a lot more adjustability and it's easier to position the cleats but you will be required to do a little more pedal maintenance (lube) than with look or shimano. I've had them all and I now much prefer speedplay because I have some needs in pedal side to side spacing (Q factor) that cannot be accommodated with other systems like Look or Shimano. In most cases, road pedal systems are a case of "tastes great/less filling."

Using regular shoes on typical pedals is not great. They are not meant for that kind of narrow pressure on your foot. If you are doing any real mileage, at some point, you'll regret not having the stiff sole and platform that a pedal/shoe system gives you.

J.