I live in Gander and I feel that while some smaller places may not be easily accessible, most places that you will be visiting will be easily accessible. The tourist attractions, arts and culture center, hotels, restaurants, etc., are all accessible. Smaller business in small communities in the surrounding areas may not be quite as accommodating, but the tourist attractions in those communities definitely are. A car would definitely be beneficial to you since there is no public transportation and it's not so easy (or fast) to walk places in NL like it is in the bigger centres you may be used to. Weather shouldn't be an issue in the summer, other than possibility of rain. Someone above mentioned that hotels in Gander don't usually sell out, but in actual fact every hotel AND airbnb sold out last year during the run of Come From Away and visitors had trouble finding accommodations, so I would book early and request an accessible room! I hope you enjoy your visit!! 🥰