Nokia 1 has single core ARM Mali-T720 MP1 GPU, which has 550 MHz frequency.
Yes, Nokia 1 does have the Google Assistant in-built.
Yes, Nokia 1 does have the MicroSD card slot. You can use MicroSD card of up to 64 GB capacity.
You can record 720p resolution videos from Nokia 1.
The Nokia 1 is an inexpensive Android smartphone, and as you can tell from the Nokia 1 review, you very much get what you pay for.