Hi & welcome, sorry to hear about the loss of your lovebird. I have lost 3 lovebirds, I know how tough it is.
1. having its wings clipped will not cause a bird to pass away. The swing being under the bird when you found it could indicate that he passed away and fell off of the swing and the swing came down after him. Wings clipped along will not cause a birds death.
2. If your bird now is fully flighted and comes BACK to you when flying, than that is good. A lot of people strive for this behavior with a fully flighted bird. Does your current bird who is fully flighted also exhibit good behavior? If so than I dont see a wing clip as necessary. A lot of people clip to curb bad behavior or to prevent their bird from flying scared and crashing into something. it sounds like your bird is pretty well behaved when flying so I dont think at this point a clip is necessary.
3. As far as the biting goes, when he does it you slowly hold his beak, say "no bite" and remove him from the situation. I have a mole on my neck and when Neko (painted conure) bites it I move his head away and say no. He has learned not to do it but every now and then he does and I just continue to tell him no and moving him away. if he gets particularly bad I move him back to his play stand. He loves being with me so he knows this is punishment.
4. Getting him back on your hand from your shoulder may be the most difficult. I take it he does not step up for you? My second lovebird would do this and I would have to just transfer him from my shoulder back to my cage. If you really want him on your hand you might just have to force him to step up or resort to grabbing him. Neither are ideal. He probably just doesn't want off your shoulder but if you REWARD him when he gets back to your hand he will learn that he gets treats for GOOD behavior and will probably do it more.
Hope this helps!!