Not sure how Macron is thinking of dealing with no party support. I'm no expert on French politics but I would imagine that the way he will lean in his policies will also be decided by who is open for cooperation.
French politics aren't that locked to parties.
Parties are created and destroyed based on the needs. A lot of moderate right and moderate left people have expressed that they were ready to support him instead of their natural candidate. Some technically can't (because of primaries) but probably would, and can change their stance after the elections.
I don't doubt that Macron will be able to put candidates everywhere for legislatives elections. Some coming from both side, although many "new" (so that it angers noone... again, it's the general strategy, that's fuzzy logic applied to politics). Since it's largely a "winner takes all" in each place, a small edge can give you a strong majority, and often, after the presidential election, people are willing to give the president a chance.
So yes, he can. He may not have a majority alone (although it's possible). We'll have to see how he deals with it IF he's elected and depending on the legislative results.
And well... Macron is already left AND right. He almost ran for mayor in Le Touquet as an unofficial LR candidate (main right party) but had to give up because he was in secret a PS supporter (main left party). Talk about working with both sides
It's far from uncommon for people in France to move.
And, well... Wasn't Trump a Clinton supporter in the previous election ?
