I've Chosen my niche! Passion over revenue - beginner help on keyword tools and theme

Hi Warriors,

If you've seen my introduction post, you'll know that I've been out of the game for 10 years and need to familiarize myself with the new world of affiliate marketing. However, I'm diving in head first and excited to enhance my knowledge.

As per the title of this thread, I've chosen my niche based on personal passion instead of soulless revenue. The niche chosen is in Travel and will focus on "off the beaten path" and "adventure". The idea is to guide travellers on visiting countries/cities that aren't on peoples usual list due to lack of information/fear of safety and the unknown. With that being said, I'd like to know if it's wrong to include some main stream travel locations/guides. I believe being a mix of "off the beaten track" and "main stream" can broaden my audience but I risk losing interest from my main target of adventure travellers - which will be easier to rank for.

Also, I've been using the google keyword planner and was wondering if there is a better research tool to find keywords and help choose a domain name... I'm open to paid and free tools - if you have any suggestions, please share!

Lastly, I read that StudioPress themes for Wordpress are great for SEO. Can anyone verify this as true? I'm leaning towards the theme below but would like some feedback before making the purchase.

https://my.studiopress.com/themes/essence/

If you read this far, thank you. Looking forward to any feedback you can provide.

Cheers,
Mike