Upwork or other platforms like it are always a good option.

A great place to start would be angellist.com. LinkedIn would be another good resource for finding investors and VCs.

Yes, just record the video on the device of your choice and then upload that same video to both your TikTok and YouTube accounts. If you are wanting to add existing TikTok videos to your YouTube account and you no longer have the original video on your device you might try a platform like repurpose.io.

Some of the easiest websites to design and manage in my experience are Squarespace.com and Wix.com. Shopify is also a good one especially for Ecommerce.