You go up a level at the moment you gain the requisite amount of experience, no matter when the experience is given. The real question is when the Game Master actually gives out the experience. I've seen everything from after every encounter, to after each session (the most common from what I've seen), to after an adventure is complete.
So the bottom line is that you don't need to rest, but if you're GM wants to play the game that way, then that's the way it is (e.g. he's only going to give out the experience after an extended rest).
This is explicitly outlined in DMG 1 on page 121:
XP Per Encounter
Some DMs prefer to give XP after every encounter. ... Others prefer to award XP when the characters stop for an extended rest or at the end of a gaming session. It's purely a matter of personal preference but be mindful of the pace of the session. Don't stop to give out XP if it's going to bring the game to a halt at a tense moment.
Leveling Up
Soem DMs let characters gain the benefits of a new level as soon as they ahve the required XP to reach that level, while others prefer to wait until the characters take an extended rest or even until the end of a session before letting characters level up. That decision is entirely up to you (the DM). ... If leveling up would shatter the pace of the session, put it off until they take an extended rest at least.
The canonical "true/current" version of everything is found in the compendium, here (subscription required to use as more than an index).
There are, at present, three current "Cleric" classes you can play. I define a cleric class as anything that counts as a cleric for purposes of feats, beyond that of multi-class.
There is the "original" Templar Cleric. Recently renamed from "Cleric", the templar cleric is the cleric of healer's lore, lasers, and optional pacifism. A number of its powers have been errataed to reflect appropriate range and power. (Otherwise it was a rather superior controller.) The most important errata is the limitation on buffs to surgeless healing, and is the only critical errata to apply. (Basically the rule of thumb is: if you don't pay a surge for it, it doesn't get buffed by anything)
There is the essentials Warpriest. The warpriest is a simplified melee cleric featured in the essentials books. It uses domains and features the current domains of death, earth, storm, and sun. Death is debuffy, Earth is forced movement, storm is buffing, and sun is glowy (that's a shocker right there...) I am not aware of any major errata that must be applied to the class to correct game-breaking brokeneness. The warpriest shares few mechanics with the Templar, and should be considered a different class that shares feats, general role, and PPs.
There is the PH3 Hybrid Cleric that stinks. Avoid it. But it's there. There are no major updates for the hybrid cleric.
Sources of truth
The most important source is DDI. The second most is the Rules Updates. Everything that appears in a book is compiled and/or changed in those two. DDI is more authoritative than the rules updates because sometimes wizards engages in "stealth nerfs" (see Divine Oracle) that aren't loudly announced and may or may not be reflected in the rules updates.
Best Answer
Partial cover and concealment are identical to cover and concealment.
It's a confusing terminology change that happened part-way through 4e's lifespan, not the addition of an extra level of cover and concealment. The modifier "partial" was added to 'normal' concealment --probably in a well-meaning effort to clarify things-- and both the Rules Compendium and the Online Compendium parenthetically note that it is "sometimes simply called 'concealment.'" (RC 222)
The Online Compendium's glossary entry on cover still hasn't appended the modifier "partial," nor does it note that this word might sometimes be added, but the Rules Compendium uses the phrase "partial cover" and adds that it is "sometimes simply called 'cover.'" (RC 220)
Keep an eye on "superior" and "total," too.
There is equal potential for confusion in the upper echelons of cover and concealment: better cover is called "superior cover," while excellent concealment is "total concealment." I see no particular reason these two similar effects should have different modifying terms, and am surprised that only one item (the Nightmare's Keen Senses from DR 393) is currently confused by this (according to a search of the Online Compendium at the time of this post).