First, are you using the suggested adaption in the book for shadowcraft mage (The one where you don't have to be a gnome)? If so, I would be something other than a gnome. Like an Illumian, that works well with shadowcraft mage. A post on the handbook suggests Dragonborn Illumian, which does seem like a good choice if that actually lets you grab both improved sigil(Krau) and Practical Metamagic.
Feat-wise the shadowcraft mage handbook has a lot of good suggestions. You might want to look into early entry tricks for master specialist (illusion).
But let's talk spells. I had built a shadowcraft mage cohort for someone once, let's see if I can find my list of suggested spells to look at for copying..
List of Spells to copy often:
1st:
2nd: Craft Magic Tattoo, Wind Wall, Glitterdust, Blood Wind (Target’s natural attack can be used as a ranged weapon)
3rd: Sonorous Hum, Caustic Smoke, Glowing Orb, Unseen Servant Hoard, Sepia Snake Sigil, Greater Mage Armor
4th: Black Tentacles, Solid Fog, Resilient sphere, Magnetic Pulse, Sparkles(10ft/level sparkly), Doom Scarabs (60ft cone, Will half, temp HP for beating SR!)
5th: Wall of _____(lots of walls), Streamers, Phantasmal Thief, Sending, Slashing Dispel
6th: Contingency, Wall of Iron, Shalantha’s Delicate Disk
7th: Mage’s Mansion, Wall of Eyes, Ice Castle, Submerge Ship, Amber Sarcoughagus, Forcecage, Stored Lighting Bolt, Phase Door, Instant Summons
8th: Trap the Soul, Telekinetic Sphere
9th: Iceberg (No save 20d6), Instant Refuge (Teleporting), Blinding Glory, Summon Elemental Monolith, Summon Monster IX (Use BOED options), Summon Golem, Genius Loci, Reality Maelstrom, Crushing Fist of Spite, Binding Chain of Fate, Sphere of Ultimate Destruction (Destroys walls!), Gate (Only the travel option, can’t call a creature), Tidal Wave (Needs Water), Burst of Glacial Wrath (Fort half Cone, turns living foes to ice at -1hp or lower so it can’t kill)
Towering Thunderhead (40ft radius windwall/Fog/Slowdown/More)
Other notable spells that can be copied:
2nd: , Kelgore’s Grave Mist
3rd: Sonic Shield, Wingblast
4th: Dweomer of Transference(SP->PP), Firestride Exhalation (30ft 8d6 port cone)
5th: Lord of The Sky
6th: Luomund’s Carriage thingy(Not name of spell), Entomb
7th: Choking Cobwebs
9th: Detonate, Prismatic Deluge (40ft cylinder, 80ft tall), Deadly Sunstroke
..I don't have the book locations for all of those, unfortunately. And some of the really neat ones are quite obscure <at least based on my vague recollection>. Sorry about that. Anyway, remember that all shadow illusions are standard actions! That really improves some of the spells on that list. Also, some of the above spells (Like contingency) might need to be 100%(or more!) real before they work properly.
More on the Summon Monster IX: The Book of Exalted deeds adds a bunch of neat summons. Namely, summons that can cast arcane/divine magic. You can eventually just poof out a middling cleric/wizard on command, which is good for when you need someone to use a staff or something to cast a spell from your banned schools.