My dad was diagnosed with diabetes. And we are so new to this. Have some questions.

So My dad (50) was diagnosed with diabetes few days ago. Readings were 180 early in the morning no breakfast. and 208 in random timing evening. Doctor gave some medicine (Metformin hydrochloride). He just said to not take foods like rice, potatoes etc But he didn't say much about other things.

I did some googling and decided some foods with low GI and more fiber, etc. (whole wheat, pulses, fruits ) And my dad want to completely remove carb foods from his diet. Is it advisable?

I read on this subreddit that not eating food after insulin is not good since it can lower sugar level too much, but my dad don't take insulin, I am not sure if I can apply this to his medicine so I don't know if cutting out carbs completely is okay for him since his sugar is not too high (correct me If I am wrong).

Is there something like as he will get old his sugar level will keep on increasing (his random is 208 but he knows some who have 350 and take injection)? Also is there something I should know how to take care of sugar levels properly. Thank you.