I would invest the bulk of your budget into Facebook Video ads.

Test at least two different videos (about 1 minute in length each) at $1/day. Take the one that performs better (10-second views, clicks, conversions, etc.) and then scale that up to whatever daily budget you can afford.

Consistent Twitter posts (Images, GIF's, Videos) to the right hashtags will be one of your best bets.

As per above, Steam keys would be one of your best options.

I wouldn't worry about how many followers/subscribers they have. You can use a service where they can "unlock" content with a tweet/share, so they could then "unlock" a form to request (or confirm) a key through that, so that you gain at least some benefit.

Here's one tip for Twitter Video: upload your video through "Media Studio", which you can find in the drop down menu under your profile picture. You can then add a call-to-action link to the video itself, which can lead views to your game's website and/or Steam page.

I can't speak for the value of GameJolt specifically, but in general, it would be wise to have your game on as many distribution channels as possible (like you are with itch.io and Gamejolt).

You do have a valid concern, which is that the bulk game marketing efforts result in sending external traffic to a 3rd-party site. If you are going to do this, I'd advise that you use a link retargeting service like Rebrandly to keep track of link clicks and to embed your Facebook ads pixel to the link itself.

Ideally, you should see about selling your game directly off your website, for a few reasons, mainly control and analytics. PatchKit has a distribution network to handle the content (game downloads and patches, hence the name). You'd then need to find a payment processor.

Both Twitter and Facebook have poll options for tweets/posts. On Facebook, I would recommend you form a group, and create a poll within that. You could also post in other game groups on Facebook.

As far as surveying goes, there are multiple services you can use. Google Forms is free to use.

You can get traffic/leads to the survey/poll a couple of different ways through Facebook ads (starts at $1/day).

For data and statistics, Steam Spy will have data on PC games, and App Annie will have data on mobile games.

I would invest the bulk of in Facebook Video Ads.

A small portion of it ($50) could also pay for social media tools, like Edgar, for an entire month.