Sniper/pistol hybrid - never played one, I would guess pistol is a poor fit due to the need to pump DEX. On the other hand this is still a sniper build so it shouldn't suck.
Better than you might think.
You only need 7 DEX for Gunslinger, that's completly enough. 4 attribute points sounds like a pretty big investment, but it's not like you don't get other benefits out of it- 4 bonus initiative and bonus skill points if you decide to invest in lockpicking/pickpocketing/throwing/traps. I usually take lockpicking, throwing and traps so it saves me a ton of skill points, especially considering those skills are of "needs to be high enough" kind rather than "needs to be maxed every level".
Speaking of initiative, that's the biggest selling point for me. Having really high initiative in addition to stealth is just great. That +7 bonus from Gunslinger is something that can't be replaced. I tend to go 6 AGI and 7 DEX, with Paranoia I end up with 30 initiative. I genuinely can't go back to SMGs or ARs for that reason- they do deal more damage, but I don't feel like I need it considering how much damage sniper rifles deal in the first place. I'd rather improve my odds of starting the fight on my own terms regardless of the situation. Keep in mind this is coming from someone who never savescums and tries to keep the death count as low as possible, I guess it's not going to nearly as useful if you do savescum.
Another thing to consider is that Sharpshooter bonus critical damage applies to pistols. All proper sniper builds will have Sharpshooter and Critical Power, so pistols will effectively have 75% more critical damage than SMGs and ARs (only 60% if using Neo-Luger). This becomes even more meaningful considering sniper rifles get a huge benefit out of stacking critical chance (critical damage still being a priority). Smart module and A-A scope give enough damage as is so imo seeker goggles are a much better choice than smart goggles, add Recklessness and Focus Stim, you should end up with around 47% critical chance with the sniper rifle and 44% with the pistol. Or up to 100% in certain situations with Ambush.