The basic three books -- Player's Handbook, Dungeon Master's Guide, and Monster Manual -- will give you what you need. You can find hard copies if you look online, possibly as a gift set. If you're experienced with other editions, you'll notice the lack of barbarian, bard, druid, half-orc and gnome options; those were included in Player's Handbook 2, and psionic classes of note, particularly the monk, were the focus of Player's Handbook 3.
Be aware that there are a fair number of rules updates that affect these. You can find the full list here.
For the Essentials line here's the breakdown of what I think you'll want if you go in that direction: the Dungeons & Dragons Fantasy Roleplaying Game Starter Set, as an optional tutorial; the Dungeon Master's Kit, which is the equivalent of the Dungeon Master's Guide; the Monster Vault; and one or both of Heroes of the Fallen Lands and Heroes of the Forgotten Kingdoms, which give player options. The first three of those were boxed sets, and you'd wind up with three or four adventures, some dungeon terrain tiles, a ton of tokens to use instead of miniatures, and a DM screen; these things are not included with the digital releases, however, so you might need to turn to external resellers. You may also want the Rules Compendium -- it has some rules not covered by the DM's Kit, but is more of value to people who have the core books and don't want to look up errata to rules.
The advantage of Essentials is that it's an easier entrance point, particularly if you're familiar with an older edition. Also, it doesn't have a ton of errata.
If you buy either group of books and later want to use material from the other group, that should be possible without any fuss.
Finally, I'll agree that the Dungeons & Dragons Insider subscription is a good purchase. You did get (in 2010) access to an online database containing every rules option from every source; you get a character builder, which also has all the options (Windows and Mac only); and you get daily articles. (2021 update: subscribing to DDI is no longer possible and the content needs to be picked up piecemeal. Dragon magazine is still available)
Monk's +3 unarmed proficiency bonus is only added to weapon attacks, not monk "Implement" attacks. Monks are confusing.
The difference is in the keyword of the power.
Drunken Monkey has the following keywords: Full Discipline, Implement, Psionic
The one we care about is "Implement"
Because monk attacks are implement attacks, they do not use weapon proficiency. Instead, they use Half-Level + Dex Mod for attack versus Will, and 1d8 + Dexterity modifier damage (note lack of half-level) for damage.
To increase the attack mod, you need to invest in feats like "Ki Focus Expertise"
The Melee Basic attack on the other hand would have the weapon keyword. Therefore you would, on an opportunity attack, use +3 + Half Level + Strength Mod versus AC.
Best Answer
It means you roll your d20, add your Wisdom modifier, and compare it to the enemy's Will. You don't just compare your Wisdom score to their Will - that isn't what's used here.
On Scores and Modifiers
If you have 20 Wisdom, that's your wisdom score. 20 wisdom gives you a wisdom modifier of +5. The wisdom score is not used in the roll at all. Aside from being used to calculate the modifier, ability scores are very rarely used directly. If anything ever actually uses your wisdom score, not just the modifier, it will explicitly say so with the words "Wisdom score" or something similar.
On Attack lines
In an Attack line, the "X vs Y" is, in general, an ability (Strength, Intelligence, etc) vs a defence (AC, Will, Fortitude or Reflex). You always roll the d20, add the specified ability's modifier to the roll's result, and compare it to the specified defence. If the result is equal to or higher than the defence, the attack succeeds.
I'm sure somewhere your Red Box's books should explain how to read a power card and explain the nature of all lines that will show up on one, though not possessing the Red Box myself, I couldn't tell you where or whether it does. The regular (non-Red Box) Player's Handbook does at the very least, and I imagine the Rules Compendium does too.