Sure bro. you can ask as many questions you want before making the purchase. Will try my best to assist.
Safe to buy with warranty always. The model number ends with 1 or 2 digits that let us identify the country whether india or other country.
For example if its india then the model number ends at HN.
You can see the complete list here in this article,
Mostly sellers inform before selling imported units. Just personally you can do this check too.
Storage selection depends on how much content you are going to store on device bro. for more photos, videos and files 256GB is good choice.
But make sure to backup important sensitive files always to Google Drive or iCloud to avoid any data loss. Electronics can fail sometimes and we should not end up loosing the data. so to avoid such issues taking backup periodically like few months once will prevent data loss.