I'm sorry but I respectfully have to disagree with you on every point.
- The OP is talking about Home Automation and already has a capable server (HA), so any need to directly control/talk to actuators/sensors is a failure.
- I would consider IFTTT a last resort and only use it if I want to use something that ONLY supports IFTTT.
- I agree with using the one that suits you best, but I would call WiFi a last resort. However anything beats going through the cloud.
- I would advise against messing with the FW unless you need to. That's how you break compatibility (and sometimes hardware).
I would recommend any sensor/gateway/echosystem that allow local control and that you are in charge of upgrading.
If it ain't broke, don't fix it.
I'm sorry if I sound harsh but since the OP already has a HA setup I feel your suggestions are completely wrong.
@jo34l5 Design you HA setup with internet independency in mind and you'll probably end up with a very stable solution that does what you want, when you want it.
You said you haven't spent to much time on the rules yet, this is where I would recommend you spend the most time.
avoid cloud based sensors at all cost for security and future proofing reasons.
and stability, and reactivity/delay, and.. I think this list could be endless