therere lots of crypto marketplaces nowadays. I guess its not a big deal to find the suitable one. Unfortunately I cannot advice you because i prefer using classic marketplaces.
no . crypto based marketplace are actually verry rare today due to the crypto adoption which isnt big enough .
i know some site online that accept crypto payments but those site are seems unsecure and they are not also reputable . so i dont recomend to try them though i heard that amazon , ebay and other popular stores are now starting to have a plan about crypto partnership . you'ld better for them because they are 100% legit .
Meanwhile the best thing you can do is to trade you coins unto local currency and buy directy on physical stores or convert them unto paypal or other ecurrency/payment method that most online stores accepts .
Yes this is a good idea but the exporting of this project will be more tougher for both the seller and buyer also because than stability will made the huge part but in future we may eminently expect the changes and it will be most important thing to discuss also.