Puzzle and Dragons – What Is the Pal Points Limit

RCV is actually short for "recovery" and relates to how much healing you'll get from matching hearts together. From my guide:

Just below your team is your HP bar. As enemies attack, they’ll deplete this, and you can restore it with your team’s Recovery (RCV) stat by matching the heart orbs together.

Or the PAD Wikia:

RCV: The base amount of HP you will recover by matching 3 Heart Orbs in battle. This value is the RCV sum of all the monsters on your team, but the actual value in battle also adds the RCV of your friend's leader.

Generally, when your first starting out, the special dungeons (depending on what they are) can be much harder, for beginners. Think of special dungeons as special events, which arent always available, and depending on time of the week or year, are available. Depending on what your starter monster was (your first Rare egg machine pull), the special dungeons can be harder or easier. We would have to know your rank and monster box to get an idea if your ready for the special dungeons. It would be wise to get an app called "padguide" It gives you info on dungeons, monsters, events, evo material for monsters and stuff. Think of it as the encyclopedia for the game. You may be ready for some of the earlier variations of the dungeons, such as int, and maybe even expert, if you look at the guide to see if you wont get 1 shotted, or can kill the monsters before that. Although, I would not recommend doing the mythical dungeons for a while, because they are pretty much all tough descends, and even if you do have barely 50 stamina, will be a waste if you arent ready yet.