This question is on a thin line between project management and team management.
For team management I would say to put one person on the "unknown" for a couple of days to get some basic actions performed. Write all this code in a project called "unknown-playground" (in your case "selenium-playground") and commit this code to the repository so anyone can contribute.
From my experience, 3 days on an unknown is quite enough to finish a project.
This team member is declared as an "expert" on the topic and is in charge to increase the knowledge bank further as needed. Usually, talking to an external expert/vendor is not required, but very recommended. That includes asking questions online, which is my personal favorite.
Please note - this person writes to the playground project. I recommend having the rest of the team use the code snippets from the playground project to use in the real project. Do not bind the expert to all features related to this technology, only for acquiring knowledge or they will be isolated from the team which is bad. This expert should guide the rest of the team and the rest of the team should be encouraged to use this knowledge bank as often as possible.
From a project management perspective, I think the most useful thing to do is to set deadlines on the playground project. For example, lets use selenium: add a feature - load a page, click a button. And this should be delivered internally.
I do not agree on putting more resources - usually this only generates noise rather than helps.
Appointing a single authority to lead a technical side of the project most likely proves itself more efficient to the project and the team member's self esteem.
As a team leader, I had the unfortunate experience to deal with forced deadlines on projects with unknowns. This approach allows me to make the deadline more than you'd expect.
Whatever you do, do not tackle the unknown at the end of the project or it will fail for sure. Talk about it, be true to your customer, I am sure they will appreciate your effort, perhaps they will even be able to connect you to someone who can help (happened to me once).