1. What would be the drawbacks to a minimalist electronic approach? Like simply a hand-held GPS? When visibility is good, I intend to rely on paper charts and triangulated position fixing if I need to know EXACTLY where I am. But in essence, navigating the "old fashioned" way appeals to me more than sitting there looking at a color screen. The hand-held GPS, capable of providing an exact real-time fix, would be relied on more for fog / low visibility situations.
There is nothing wrong with a minimalist approach. Your boat, your money, your selection.
I started with a simple black and white hand held Garmin. It came with a marine basemap that had every navaid in the US listed. It worked great to tell me exactly where I was (lat / long), how fast I was going, and in what direction I was traveling. It was OK at providing me with exactly what bouy or light house I was approaching, and it was poor at usability because the screen was small and the user interface was clumsy.
2. Garmin handhelds and entry-level chartplotters come with US Coastal "BaseMaps" but then it seems they want more $$ for BlueChart maps. Their site is very poor describing what one does and does not get with Basemaps and BlueChart upgrades. Basic question... do Basemaps provide enough info for safe coastal sailing in low visibility conditions, or is the BlueChart upgrade necessary?
The basemap usually contains every navaid in the US. It may contain tide information. It will not contain information on marinas. Updated charts will contain tide and current information, detailed information on marinas, and will usually display depth information like a printed chart.
While the basemap is certainly sufficient for safe coastal cruising, the updated charts do have significant benefits. IMHO, the updated charts are only useful on a larger color screen.
3. In addition to GPS (or maybe entry-level Chartplotter) I only plan to install a depth sounder. I've done enough small-boat sailing that I don't need / want speed or wind instruments (I can also get SOG from a GPS). Looking at the traditional sailing providers (Raymarine, et al) , depth sounder / transduver combos go for $400 +/-. A Wal-Mart fishfinder with thru-hull transducer is $125. What am I missing here?
The basic sounders will work OK and as listed above you can get high quality sounds for less money.
IMHO, you would be better off with a smaller, cheaper, integrated plotter / sounder unit than with a handheld unit.
The benefits of an integrated plotter are a larger screen (usually), connection to ships power so you don't need to worry about batteries, and you can't drop them overboard. Lastly, they can be easily connected to a DSC VHF unit.
When I bought my second boat I wanted a better GPS system so I bought a Lowrance M68C S Map. This is a small, affordable, color GPS and depth sounder. IT comes with a detailed basemap including depth, tide, and current information. The screen was 3.5" and easy to read. For my third (and current) boat, I wanted the same functionality, but a larger screen, so I bought a Lowrance LMS 337 CDF with a 5" high resolution color screen.
If you can afford to spend $350 or so, you can get a great GPS system.