I put the Pi 4b into a aluminium case then into a cheap waterproof box
but before I bought the waterproof box I used the box my 3060Ti came in - would withstand light rain if was caught out by the weather forecast.
Mic wise - I did go for a specifically sensitive one - a Clippy EM272
A clip-on lavalier microphone using the superb low noise, high sensitivity Primo EM272 omni capsule Rugged black anodized aluminium enclosure, metal grid, tough metal clip and 1 metre of thin flexible screened cable To use with a smartphone you can use a TRS to TRRS Microphone Adapter or a Smart...
micbooster.com
although before I bought that I was using my USB Calibration mic from my home cinema (UMIK-1) with excellent results.
There are much cheaper options than the Clippy I bought
the UMIK as a USB mic - plugged straight into the Pi but for the Clippy it needed a Audio interface/DAC - I tried a few and the gain wasn't enough. The best I've used so far is the Apple USB-C dongle (with a USB-C to A adapter) - there is noise on it (odd wavey lines) compared to some other cheap audio interfaces I used but the gain is very good and it was very cheap, the extra gain is much more useful than the additional noise I seem to get
I power the lot with 2 Anker batteries which I switch between, one a 10,000mAH which lasts about 12 hours, and a 20,000mAH one which lasts about 24 hours
I set for the very best archived results the software to record all bird recordings as FLAC, and I reckon a 256gb card will do about a whole year
much smaller file sizes if MP3s but I noticed some quality degradation