Ooo, I thought I replied to this. Yeah, person in a suit - something that big would have to be literally dragged around by you and would be a big hassle and bump around and get dirty and fall over and all that.
It would be difficult and expensive as balls to make the boar life-size, rideable, and able to walk. And I have doubts it could be accomplished by a hobbyist who doesn't already have a heavy background in robotics - it would be seriously cutting edge work if you could do it. Check this
out, you'd have to know how to program all those sensors and stuff - a cool project and all but not something to really jump into without preparation and knowledge in programming and stuff.
For a convention I think a hold-able sized one would be fine and would be cute and add to the character without inconveniencing other people.
I'd also consider your budget - that would be a LOT of faux fur in one big enough to sit on and that stuff is pretty expensive - like usually $20/y and I wouldn't be surprised if that thing is using 8-10 yards of faux fur - over $150 just in the faux fur for it without even getting into everything else.
Worbla is a thermoplastic that melts at a relatively low temperature - so you can shape it by heating with a heat gun and your hands instead of special tools or having to create sculpts and cast, et cetera. You can just paint the gems or you can get into casting resin or something like that - there are a lot of ways to accomplish these kinds of things.