Specialization and Build Plan
I focused on Divination going for Red Wizard. My guys are a TN Human Diviner5/Red Wizard3 and a TN Human Diviner5/Red Wizard 1. (Once I tally my XP bill for magic item makin', this guy's losing his Red Wizardhood.)
I did this because losing access to 2 schools hurt. Being my own party means I need backup minions; hence, I kept Necromancy for animate dead. Command undead is also handy.
Offense
My magical offense is mostly a Wand of Evard's black tentacles. A word of caution: the black tentacles in your case have a grapple check of +16 (level+size+STR 19). This is either below that of most opponents in your CR category (CR7-9) or they have some means to evade it (flying, incorporality for instance).
It may be good to have this spell as a backup in your book, but not as the main offense and definitely not for 25% of your wealth (when using create wand feat and ignoring standard wbl, otherwise the wand costs 21,000)
Spell Preps
My spell preps are uncertain. Spells I NEED or greatly want:
Level 0
-Detect Magic
-Ghost Sound
-Prestidigitation (Keep those robes clean!) In case you want to bring your minion along, the message cantrip also helps.
Level 1
-Alarm (Bug, bug, bug, bug my rope trick!) A bit iffy. The rope trick is non-dimensional, so it is arguable whether this is within the range of the alarm spell. But still useful as backup, in particular due to the long duration.
-Comprehend Languages [Scroll x2 OR my Diviner slots] Yes. Better than scroll: use a (self-made) wand (cheaper per use).
-Disguise Self [Hat of Disguise - For planar binding negotiations] -Grease (beats Epic Golems) -MAGE ARMOR! [At-Will Command Word Item] -MAGIC MISSILE! (incorporeal foes, dood!) Yes. A classic.
-Mount (cheap minion to sacrifice) -SHIELD! [Continuous Item] -Silent ImageMost versatile core level 1 spell. Sold.
Level 2
-Alter Self [At-Will Command Word Item - Wizards become Troglodytes for +6 natural AC and animated Undead become Shadows] -Command Undead (Yes, there are.) -GlitterdustVery good all-purpose spell.
-Invisibility [Wand - Avoiding targeting] A wand of this is a good idea. The duration is fairly limited, though. Try to get some continuous camouflage effects to move more unnoticed continuously, near encounters, and thus be surprised less often.
-Mirror Image (just in case) OK, but likely prefer to get other 2nd level spells for your prepared spells.
-Resist Energy [Scroll x2] Again, better to have as a wand (cheaper).
-ROPE TRICK! -See Invisibility (fills a Diviner spell slot) Yes (best 2nd level divination spell).
-WebBest core 2nd level offensive/area control spell for dungeons. Thumbs up.
Level 3 -Arcane Sight (Diviner bonus slot) -Dispel MagicYes. Prepare one/day.
-Explosive Runes (My main guy has 400 pages of 96d6 runes. My cohort purposely fails his dispel magic check.) -FlyGood, if only it were not so short in duration. Better get a flying minion, like a figurine of wondrous power- bronze griffon. 10,000 gp (you cannot yet craft it yourself), but also doubles as a solid fighter (enhance it with your mage armour and possibly other buffs). Or better yet a wand of flying (since it is allowed crafted by yourself at half the cost).
-Greater Magic Weapon (Convert junk weapons to magical, ghost-hurting shinies for 1 hour/level!) -HasteGood when you want to throw your small army into combat. Inferior to other 3rd level spells just for casters alone.
-Leomund's Tiny Hut (Force bunker) -Magic Circle vs. Evil (keeps the mind control away, and, hey, +2 deflection AC) -SECRET PAGE! (needed to get 'free' spells) -SHRINK ITEM! (Adamantium Tinfoil Hat, pre-shrunk boulders) Does not work by RAW. And if your DM allows this, he could just say: you win. Yawn.
-Stinking Cloud (Evard's black tentacles companion spell!) -Tongues (Diviner forced pick) Good (See above).
Level 4
-Arcane Eye (Diviner bonus - I can gather local info!) -ANIMATE DEAD! -Dimension DoorYes. Always have one escape pod like this. Would be best if silenced somehow (to be really good in a grapple or pin or paralysis).
-EVARD'S BLACK TENTACLES! [Wand] See above.
-Minor Creation (cover Undead army and their weapons in gallons of Black Lotus Extract) -POLYMORPH! -Remove Curse (backup plan) A great spell to have in the book.
-ScryingSee above.
-Stone Shape