Hi Im new!

Welcome to the forum. I agree with easttex, mine whistles at me when I get up to leave the room, if I leave then the squawking begins. Sometimes the squawk for who knows what reason. They're noisy birds by nature,some more then others. Good luck.

Welcome to you and Twinkle! Pellet-based diets are healthier than seed-based ones. Try introducing some pellets to Twinkle, along with a variety of vegetables, both fresh and cooked. Fresh green peas are a favorite of lots of parrots. Sweet potatoes, carrots, kale, dandelion greens, broccoli, cooked green beans and many others are good for parrots. Cooked grains like quinoa and barley are good too, as is cooked pasta. It can take time for a Quaker to accept new foods, so you'll need to be persistent and be prepared to waste  some food. ZuPreem Fruit Blend pellets are popular with many QPs, but you may need to experiment a little to find out which pellets Twinkle would like best.

Here is some information from the companion site, Quakerparrots.com, about converting to a pellet diet

A DNA test, which can be done by a qualified avian veterinarian, is the best way to determine whether a parrot is male or female-- unless, of course, the parrot lays an egg.

Greetings to you and your little one!! You have already gotten good advice on this thread-- I will simply echo the importance of transitioning away from a seed based diet to a pellet based diet. Quaker parrots are very susceptible to fatty liver disease, and seeds are quite fattening. Also, seed based diets do not adequately supply necessary nutrition. And you definitely want to introduce as much fresh veggies/fruit as you can, as even pellets do not provide everything they need.

Feel free to ask any questions you might have!! Everyone here will be happy to help.

Fluffing can mean several different things, and you have to look at the bigger picture to know what is meant.  If the bird is sitting on the bottom of the cage fluffed up, he is showing signs of illness.  If he is feeling threatened, and looks very alert, he's trying to make himself look as big and threatening as possible.  What I assume you are seeing is fluffing as an indication of relaxation and contentment.

You're asking good questions; this one in particular.  Learning their body language is really important in keeping a good relationship with your Quaker. 

I will answer as best I can.  Probably others will be able to help, too.

1) Maybe.  Flying birds build muscle around the breast.  It's a good practice to monitor their weight regularly.  Get a scale that uses grams, and weigh him once a week and watch for significant changes.  Weigh him at the same time of day.  Before breakfast, after a poop, is ideal.
2) If it sounds something like purring, it's contentment.
3) Head bobbing is normal.
4) Definitely.  Step up is very handy, and the training process itself is very bonding in a positive way.
5) As far as his leg goes, you would probably have to have him examined by an avian vet.  It's a good idea anyway to have a vet for Twinkle and get a health check now and then.
6) He could be molting.  Have you seen the feathers as he has shed them?  
7) Nail cutting is up to you.  If you do, I recommend you have a vet do it first.  It's easy to go too far.  Many of us rely on special perches to keep their nails in check.
8) They don't actually shed their beaks, though bits might peel off.  They grow continuously, and birds use rough surfaces and hard foods to help maintain them.  That's another thing the special perches are good for.