Hi @dphelun,
– 1) no idea ! It depends of what you know about WP and BP, coding and templating
– 2) see 1…
– 3) in theorie yes. In real life… check the forum… and point 1.
Don’t buy a theme before you tested your project with all plugins and fonctionalities correctly working on a WP+BP default install. Use one of WP’s default theme, ie. Twenty Sixteen or Fifteen. Or even all coming with WP
This tests should be done on a test site (locally or online, but not on a production site)
Default install, because it’s the only waranty for you and the project to work properly in a respecfull environment of WP standarts. Once ok you can jump to a premium theme if you estimate it is worth. That said many free themes are just ideal too.
I would just warn you to avoid frameworks and page builders- specially because BP doesn’t use WP pages like WP does. Focus on the theme itself, and not on plethoric theme functionnalities. Theme is for layout. Plugin is for functionnality.
About Themes
you will find a lot of themes on the net. Most with nice pictures and impressive list of functionnalities and prices. Problem is that this marketing arguments rarely fit with a project. And if you’re unable to customize it, you go towards weird issues and will be lost in no time.
About plugins
Like for themes and of course your technical level.
From what you tell, i would consider WP Job Manager and his (premium) add-on for BuddyPress.
Messaging is included in BuddyPress, even if it is not exactly meant as instant messaging.
But test the message component first as is before going further. And keep in mind that less is more.