I've mained Dynamo for quite some time now, and here's the advice I can give:
1. Quick Respawn is viable for a lot of builds, it depends though on what else you're running. From my experience, Dynamo is much more effective with Ink Saver main. It guzzles ink like there's no tomorrow, so I'd highly suggest prioritizing that. If your other 2 slots are open, Quick Respawn is worth running because Dynamos are often glass cannon-style weapons, so your K/D can really vary.
2. I prefer the Gold, but it depends heavily on your play style. Gold is offensive and all about turf coverage (which is hugely important in Ranked, don't let anyone tell you otherwise), vanilla is extremely support-focused. If you tend to stick behind the front lines of action and go for more passive support, vanilla's a strong option. Sprinklers are amazing for warding enemies away from towers as well as zoning, and Echolocator always helps your teammates. If you're a more aggressive player and tend to go for heavy pressure pushes, however, Gold is the way to go. Splat Bombs are useful in a ridiculously huge amount of scenarios, and while Inkstrike is mostly useful for Splat Zones (for instant reclaiming), people underestimate its handiness for pressure / protection as well. What I personally like to do is traverse through my own Inkstrikes and fling from inside the strike, because opponents won't be able to see you. If the strike doesn't take nearby foes out, your hidden flings will.
3. The biggest weaknesses are, by far, slowness and maneuverability. And, following the big nerf, the lagtime on ink refill, which can take serious getting used to. If you're fairly new to the weapon, I'd prioritize getting very accustomed to the fling time (1 full second, which can sometimes feel like minutes in Splatoon), ink refill lag and general mobility. Aim your flicks, because oftentimes having to try for a 2HKO instead of the 1HKO spells disaster. Dynamos are NOT standard rollers. As where ordinary roller users are accustomed to flick-spamming when enemies get close, with Dynamo every fling eats time so you'll need to assess when it's wisest to fling, and when you should focus on fleeing/repositioning instead.
You hit the nail on the head, chargers will absolutely be your worst enemy. Because Dynamos are slow, neon-sign targets who tend to stand their ground and fling, they are generally the very first players chargers aim for. Ink Resistance really helps, because with your slow movement speed you'll want a safe escape as often as possible (ideally, always position with some safe ink behind/around you). I'd observe beforehand if the enemy team has a charger user, and if so you'll have to plan your approaches more carefully. Although this build has divided opinions, I run Ninja Squid on my Dynamo because it hugely helps with clean approaches and escapes, which Dynamo sometimes desperately needs. It's to your advantage if the charger can't see you coming...because with the standard Dynamo approach, they almost always will. Good news is, both Dynamo subs can be effective in scaring chargers from their perches.
