Windows 10 root causes: Upgrade path or app compatibility?

The Problem:

Especially since the March 2016 update to Win10, my machine has had a continual stream of problems. The Event Viewer logs many common Windows 10 issues that Google can find 1000's of sketchy solutions for. Generally a re-boot once or twice a day will allow me to keep working. The variety of errors is huge, but typical ones include:

• Start Menu stops working
• The program ShellExperienceHost.exe / Microsoft.Photos.exe / SearchUI.exe/ ... stopped interacting with Windows and was closed.
• Activation of app Microsoft.MicrosoftEdge_8wekyb3d8bbwe!MicrosoftEdge failed with error: The remote procedure call failed
• Activation of app Microsoft.Windows.Cortana_cw5n1h2txyewy!CortanaUI failed with error: The app didn't start in the required time. See the Microsoft-Windows-TWinUI/Operational

I've noticed Windows 10 is much fussier about file associations and registry settings being set by apps, especially when it comes to types that Windows wants to be handled by its apps like Edge or Photos. (e.g. .pdf, .jpeg where I'd rather use other software). TWinUI seems to be implicated in many of these problems.

This Lenovo T440s was upgraded from 8.1 to 10 in Nov 2016. I hardly use any Mode/Store apps.

The Plan:

Re-install Windows 10 and all applications from scratch. I have about 225 items installed, and of those over 150 are from Microsoft. Re-paving this machine and configuring things will take a few days, so I only want to do this once.

The Questions:

• Are my problems more likely due to legacy incompatible software, or the 8.1 to 10 upgrade path this machine took?
• If the causes are older apps that are not truly Windows 10 compatible, what is the best way to empirically identify those apps? (Some just have no declared compatibility with Windows 10, but I need them.)
• Any other advice on getting Windows 10 working as a productive platform that includes older software?

Sorry for the length of this. I'm dreading the process and fearing the worst. TIA.

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