I've done something similar... my personnal answers :
1 - yes you could, but what I did is to keep only the path of each images inside Filemaker. Then you can keep the images inside a file server which provide a way to access them if for any reason your filemaker was down.
2- with references to images, it is fast. I've put a script that creates thumbnails that are kept inside filemaker, so it is faster to search with the embedded thumbnails and then use the path to see the larger image.
3- yes. you can use IWP (limited on a lot of things) , but I would recommand PHP