It would not be incorrect to have brass trim on only certain parts of your kit. Just be wary, if you read any reviews on illusion, the general consensus is they do good work, but be prepared for long delays and minimal communication. From what I've read, we're talking well over a year to see anything completed if they have to build it for you.
14th century is a century of immense change in armor. If you're looking to be in plate arms and legs, you're looking at the mid to late 14th century. The pig faced bascinet fits within the later part of the 14th century. You can also wear a klappvisor bascinet slightly earlier in the century, which is also found to be worn and favored by German knights much later in the century when it went out of style in other parts of Europe. You're correct that a crusader era helm would be out of place for a plate wearing knight of the 14th century. If you wanted to go early 14th century, you would be primarily maille, with some plate bits, like elbow and knee cops, and then you might be able to get away with the crusader style helm, depending on what specific style we're talking about.
Chest protection varies too. By the mid 14th century, a coat of plates would be common, an actual 14th century globose breastplate is more common for late 14th century, and a corrazzina, which is similar to a 15th c brigandine may also be seen in the late 14th. So you have some options on the chest.
For almost all of the 14th century, full plate included, you're looking at a full maille haubergeon underneath everything if authenticity is important to you. Voiders and maille faulds do not reveal themselves until the 15th century.
I can go on and on as this is my time period of interest so, let me know if you need any info.
My kit's style is late 14th century England. There are big stylistic differences between different parts of Europe, so ideally narrowing down a region is helpful.
