Thankee for the welcome,
dancing spawn!
In my opinion, Fëanor was restless and unhappy for a lot of his life. Perhaps he was always creating more dazzling and difficult-to-make treasures partly because he needed something to keep his mind occupied. He'd already explored every corner of Aman, improved their written language, learned everything he could from other craftspeople; what else was there for him to do?
I get the feeling that even before the trouble with Melkor started, he wanted to get to Arda somehow, see new things, new people, new languages, new lore, new dangers, etc. He really did feel restricted by the Valar.
The fact that he distrusted Melkor when everyone else still thought he was a great guy indicates that he had some suspicion that M was up to no good. And if one Vala could be an enemy, so could any or all of them.
*Ahem* Will try to stop rambling now.
Fëanor probably made the Silmarils for a variety of reasons:
1) appreciation for beauty and desire to make beautiful things
2) intellectual challenge (to keep his mind off problems with Valar/family? or just because he liked challenges?)
3) desire to make something that would never die or decay (possibly because of his mother's death)
4) sensing a threat in Melkor, sought to preserve the Trees' light because he suspected something bad was coming?
Of course, I could be wrong. Who really knows what went on in that mind of his?