Hi, welcome to the HA club!
Depending on your level of knowledge, I would advice you to go slow and get the hang of HA before throwing all kinds of devices and integrations on it.
Regarding zigbee, have a look at this extensive guide: Zigbee network optimization: a how-to guide for avoiding radio frequency interference + adding Zigbee Router devices (repeaters/extenders) to get a stable Zigbee network mesh with best possible range and coverage by fully utilizing Zigbee mesh networking
RPi5 or BeeLink Mini S12 PRO: have a look at this comparison https://www.cpu-monkey.com/en/compare_cpu-raspberry_pi_5_b_broadcom_bcm2712-vs-intel_processor_n100
It all depends on what you are willing to pay and what you intend to do with it.
Have you checked both prices of fully equipped systems?
The Mini pc can hold more RAM, I haven’t checked what kind of SSD interface both have.
Haffun!