If Charles the Bold would have been crowned in Trier it would have involved the Emperor and the Elector-Archbishop of Trier (Archchancellor of Burgundy (Arelat)). Simply because a self-promotion wouldn't be recognized and probably would have resulted in a real 'monster' coalition (at least France and the entire Empire) against the upstart duke.
And about the names of a kingdom, Brabant was the heir of the duchy of Lower Lotharingia (they still were duke of Lothier and they also ended up with the rival duchy of Limburg) as such Brabant wasn't that minor among the 'countries' in the Netherlands (but could be considered the premier duchy of the region). Although admittedly the Burgundian dukes prefered Burgundy, Lotharingia and Frisia (Friesland) as their new kingdom. Like I mentioned earlier the county of Holland and the duchy of Gelre had a claim on Friesland/Frisia.
And looking to the Burgundian promotion from the position of the emperor, who had to give Charles his crown, a kingdom of Friesland/Frisia and even Brabant is far more likely than Burgundy; maybe (and I mean maybe) Lotharingia could be possible, but this isn't a likely outcome.
And about the marriage of Mary and Maximilian, this probably isn't butterflied away on the contrary the negotiations about his crown and the marriage of his daughter were all part of the same negotiations. IOTL when the Emperor left Trier in 1473, Charles reacted by ending the marriage negotiations with the emperor. ( Before the dead of duke Nicholas of Lorraine in 1473, he also seemed to have been considered a potential husband for Mary the Rich). When Charles died IOTL, Mary still wasn't bethroted and could choose between Maximilian and a son of Louis XI, who had been the rival of her father. Mary ended up choosing for Maximilian and their short (5 year) marriage seemed to have been happy, IIRC there is an anecdote that they were secretly earlier wed by an ordinary pastor (priest) before their official wedding.
I think your probably right about Maximillian... If Charles wants a Kingdom he will need the favour of the Emperor so that marriage would probably still be on....
but if Margaret of York were to have born a son and potential heir then perhaps Nicholas of Lorraine's pursuit bears more fruit earlier, failing that there is Rene II which might improve the situation between the two to the point that there is no war between the two and the Austrians and Swiss mercs don't enter the picture.