Two things here.
On the matter or crowd size: Trump's organizers aren't dummies. They know what the approximate size of the crowd will be and then they will pick an appropriate venue where they predict they will have to over-stuff it to make the crowd size seem much larger than it really is.
On the matter of Trump making a rabbit turd look like a mile high pile of donkey-doo: Hey, he's Muhammed Ali Cassius Clay playing rope-a-dope with the media waiting for the media to tire itself out from throwing all those factual blows that seemingly bounce right off of him (as far as his supporters are concerned) and then when the media is tired, frustrated yet full of blood lust, they will make the occasional faux pas and give Trump the openings he's been waiting for.
Cassius Trump takes the cue and delivers a flurry of haymaker blows making the media pay in blood and brain matter for every single mistaken syllable "they lied about". Without fail, after totally ignoring the constant factual reporting that makes Trump out to be the inept habitual liar that he is, his supporters launch out of their lazy-boys and scream bloody murder about how the media is totally going after their beloved Trump as if the media were personally going after them instead.
Trump then stands in the center of his imaginary ring, waving his arms high up in the air luxuriating in the adoration of the whole grateful nation that he is the undisputed world champion of, exactly where he knew he was anyway.