I'm not going to tell you that you absolutely shouldn't go with the 530 or 530W, but I do want to be sure that you understand the limitations and downsides because the installation itself is expensive regardless of what you install, so you want to be sure that you're happy with it for a long time to come. Here's a few things to consider:
No this will be my only plane, first, last. After researching all the information everyone has flooded me with (Thanx BTW) I find the research keeps pushing me back to the old Garmin GNS-530.
530, or 530W?
Garmin has already ended support for the 530, so you should consider having at least one spare on hand in case it breaks... Not so cheap any more.
With a 530W, you'll still have support for an indeterminate but likely relatively short amount of time, so you'll likely be in the same boat eventually. However, if you get a 530W, you can also go with the slightly-cheaper Stratus ES transponder instead of the ESG.
It's unfortunate that there isn't a better large-screen option at a bargain price that isn't as old as the 530. The only other idea I had there was an Avidyne unit, but the 540 is nearly as expensive as a Garmin 750... And while the 440 would still allow you to use the Avidyne IFD app on your iPad to give you the "big screen", even that is probably well out of your budget.
So:
1) The newer units are all small, with tiny displays and I have old eyes.
2) the newer units are all touch screen and I'm just not found of in a plane bouncing around the sky
3) They all want to use BT and broadcast to another device, I'd rather it be all in one
A couple of other things to consider:
1) A big screen doesn't necessarily mean bigger text... And newer screens are brighter and higher resolution, so even if the text is smaller it may be easier to read. Make sure you find a way to look at a GNS as well as one of the newer GPS units, preferably as side-by-side as you can manage (your avionics shop may be able to assist with this, or you may be able to find local owners with both types willing to meet with you at the same time).
2) Try it before you knock it. The "bouncing around the sky" was always the knock that other manufacturers had after Garmin came out with the GTN (650/750) series touchscreens, but do you know how many companies are building aviation GPS navigators without touchscreens now? Zero. It's just not as big of a deal as you'd think, especially since they all provide ledges to rest other fingers on to stabilize your hand if necessary during turbulence.
3) The "using BT and broadcasting to another device" doesn't mean they have to do that. In the setup you're talking about, in fact, the only place you'll be able to get a weather radar depiction is on your iPad via the Stratus ESG. The 530 will not display weather from the Stratus ESG. While a GNX 375 *can* send weather to your iPad via Bluetooth, it will *also* display it on its own screen. You'll also be able to plan a flight at home on your iPad, and send it to the GNX 375 when you get to the plane, whereas with the 530 you'll either be doing a bunch of knob-twisting or you'll have to add a FlightStream 210 to your install (I believe this will also only work with the 530W, not the 530).
Finally - Be sure you get what you pay for when it comes to used avionics. Only buy items that are yellow tagged and have a warranty of some sort, or you may find yourself buying another one in pretty short order.
Look into the PS Engineering stuff instead of a used Garmin. There's no specific benefit to a Garmin audio panel, and IME the PS Engineering stuff is top notch. Looking on eBay at the going prices of the GMA-340, you should be able to get a brand new PS Engineering PMA 6000B for the same price.
3) King KI-209A VOR+LOC+G/S
This is just an indicator, not a nav radio - Presumably you're hooking it up to the 530? Why? For a VFR-only install, this doesn't do much for you unless you're planning on doing VOR navigation.
5) Keep the KY-97 for Com-2
Again, be sure you get this refurbished. All of the electrolytic capacitors should be replaced, and if any of them are already leaking (which is fairly likely), get the board cleaned off as well.