It's kinda hard to say what's the upper limit for acceptable attack bonus/Armor Class without knowing the kind of stats the characters will have and what you're permitting. Attack bonusses and armor class will also vary widely depending upon the characters in question.
Using some characters I've seen, these are some things you can probably expect on a 28 point buy.
Armor Class:
Ftr 2/Wiz3/Spellsword 2 (or Ftr2/Wiz 5)
+2 Mithril Chain Shirt, +1 animated large shield, shield spell, protection from evil spell, 14 dex (16 to 18 with Cat's Grace) and dodge. AC 30/31 to 32/33
With Expertise: potentially 37
With Expertise and Haste (Ftr 2/Wiz 5): up to 41 (higher if gnome or halfling)
Alternately:
Ftr 4/Bbn2/Sor 1
+2 Fullplate, +2 large steel shield, wand of shield, ring of protection +1, amulet of natural armor +1, Dex 12
AC 33
Without a Shield Spell:
Ftr 7
+3 fullplate, +2 large steel shield, amulet of Natural Armor +1, Dex 13, Dodge
AC 27
(This will go up to 30 if the character gets the cleric to cast shield of faith on him)
Attack Bonus
Half orc Ftr 4/Bbn 3
18 strength, +2 greatsword, weapon focus, weapon specialization
+14/+9 for 2d6+10 damage
raging +16/+11 for 2d6+13 damage
With Bull's Strength bless, and prayer, this will naturally look uglier.
Alternately (although this is a 30 point character)
Elf Clr 7 (Shevarash--although Solonor Thelandira would do)
BAB +5, 16 Dex (+3), +2 longbow (+2), Greater Magic weapon on arrows (+2), bracer's of Archery (+2) Weapon focus: longbow (+1), Cat's Grace (+1 or +2)
+15 (+16 or +17 w/ Cat's Grace) for 1d8+4
w/in 30 feet +16 (+17 or +18) for 1d8+6
And when she casts Divine Power, Bless, and Divine Favor, this will hit +23 within 30 feet (although realistically, she'll be using Rapid shot so it'll only be +21/+21/+16)
That character, however isn't really maxed for attack bonus. Take a 20 dex, elvish fighter (buffed by his friends) for real attack bonus ugliness.
I'm sure that both attack bonus and armor class can get higher through the use of prestige classes and twisted class combinations but those are what I would expect to be the high end of what you could expect to see on 7th level characters. The characters could probably squeeze another point or two by sacrificing other stats or not buying magic weapons (the AC boosters--keep in mind this is almost practical for the fighter/mage who could potentially cast Greater Magic Weapon instead of having a real magic weapon) or really skimping on defensive items and stats (the attack bonus maximizers). If you permit characters with item crafting feats to gain a discount on items they craft themselves, you may see even more creativity.
On the whole, though, all of the characters listed above are reasonably well rounded and haven't min-maxed their attributes very much. The highest stat on any of them (before racial mods) is a 16.