I know you said you're more of an amoral criminal than an assassin, but if you don't mind the disconnect between the class name and your character concept, assassin might be a good way to go for a simpler take on an Int-focused melee rogue with some spellcasting. Ignore death attack, which is a pretty situational ability that is not going to come up all that often. Assassin has good skills, fully progresses SA, gets a number of Int-based spells (including the aforementioned wraithstrike, plus some other great options like shock and awe (aka reverse nerveskitter for scouts... love this spell), alter self, nightmare terrain, improved invisibility, clairaudience/clairvoyance, dimension door and freedom of movement), and are straightforward and easy to qualify for right out of the box. You could go full assassin 10 or you could take jump out at 7 or 8 (enough to get 4th-level assassin spells and possibly hide in plain sight, but before you lose more BAB).

Keeping the Int-focus and your Daring Outlaw idea, you could go with something straightforward like Rogue 3/Swashbuckler 3/Assassin 7/Swashbuckler +7, to end with +17 BAB, 4th-level assassin spells, +11d6 sneak attack, Int to damage, good skills, etc. With the penetrating strike alternative class feature replacing trap sense, you can still do well against enemies ordinarily immune to sneak attack, and you can still go all in with the Two-Weapon Fighting line and wraithstrike.

For spells known, I'd go with something like:
1- Shock and awe, critical strike, ebon eyes, obscuring mist
2- Wraithstrike, alter self, swift invisibility, fire shuriken
3- Nightmare terrain, nondetection, magic circle against good
4- Improved invisibility, dimension door

If you're starting at level 1, I'd recommend starting with a level in rogue (this means delaying Weapon Finesse, but your skills will be SIGNIFICANTLY better this way and you get sneak attack as quickly as possible), focusing on staying mobile and attacking at range. Then levels 2-4 you'll take swashbuckler, allowing you to pivot back into melee and giving you what you need to qualify for Daring Outlaw. Follow it up with two more levels of rogue to nab penetrating strike, and then go from there into assassin. Take 7 levels of assassin and then finish the build off with more swashbuckler.

For feats, given your book limitations, Daring Outlaw and the TWF line are all good, as are ambush feats (the best of which is Staggering Strike) and feats like Craven.

This WILL be less powerful overall than the unseen seer builds that others mentioned, by the way. There's nothing this build can do that will compare with the high-level spells those builds get access to. But it's straightforward, easy to play and hopefully checks the boxes of "amoral criminal focusing on Intelligence and sneak attack with a bit of magic" without going full on mage.