Always remember rule #1: Scoundrels break rules - and even this is more of a guideline than an actual rule.
You can play a ninja and restrict yourself to sneaking+guerilla+backstab but you don't have to. You can renounce all skills that aren't particularly roguey, but the smart rogue uses all available tools, and then some.
Scoundrel has a lot of control tools - Use them.
Expert Marksman has a great mobility tool, and another CC tool and utility tools - Use them.
Witchcraft has even more powerful CC tools - Use them.
Man-at-Arms has another mobility tool, a heal skill and another utility tool - Use them.
Some wizard spells sound very useful? - Use them.
Dex is offense and defense for a rogue, if your enemies can't hit you, you don't need to spend ability points to improve your armor or shield, so you can use those points for stuff that actually makes you more versatile. (An extra ability point per level from lone-wolf can't hurt either.)
There are enough expert marksman skills that don't require a bow to justify the ability point investment in marksman 3 to get rapture, heck, tactical retreat alone is worth the first ability point. (and frankly, I use it tactical, but never for retreat.)
Man-at-arms 1 gives you access to Cure Wounds, Helping Hand and Battering Ram, all of which are useful even with low STR.
For witchcraft you ought to invest a bit in int too, but oath and blindness are worth it, maybe you even want to dip a bit deeper into Witchcraft (3) for Drain Willpower and Mass Weakness.
Finally there is the choice between willpower/bodybuilding to protect yourself from spells and abilities, and investing in stealth and hiding at the end of the round.
As for combat tactics:
Forthright melee is for sweaty brutes with huge axes, standing far behind and hurling spells is for pansies in dresses, the rogue is the one who runs (or jumps) across the battlefield to take out (or even better take over) the enemy's mage or healer. Those that stand between the rogue and his goal, are either lucky enough to be avoided, or they find themselves stunned or knocked down, on one side the rogue running away, on the other the sweaty brute hurrying towards them with a big grin on his face.
Generally my rogue isn't a loner and stealth-killer but a team player who plays by her own rules, and while scoundrel skills play a big role, they are nowhere near her only tools, a rogue uses all available resources and finds new ones on the fly (like that burning candle that can ignite oil and poison puddles for only 2AP)
