Hello
My name is Eva, I would be interested in this project. As a final price for it I see it somewhere at 1000-1200 euro, and doable in about 1-2 maybe even 3 months. There are a lot of settings and small things that have to work before you have a proper site, and usually what happens is that there are huge times of waiting between all the material is provided. This is why I think the 1-3 months is a realistic estimation for time.
The project is fairly big, requires much more communication that the text field allows me to write. Avada is a very complex theme, would suggest to go with it. A child theme is a must, with your customizations. I would suggest to build it on stages, where first one would be to add the "stanrad" frame site, the plugins, creating the environment, stage 2 populate the forum, set up memberships, add more info to this, fine tune as much as possible, and stage 3 when the actually full blown site is up and running, with optional changes after you realize that one or another solution needs adjustment. After this you might still need a "permanent" webmaster, but most likely just to keep an eye of the site. Multi language options can be added later, paid membership also (there is plugin that connects bbpress with paid membership pro) for much more functionality. Newsletter script is either mailchimp or mailpoet.
I would suggest the stage 2-3 to be built as hourly project, especially if you already learn how to add content. hit me up for a chat.