The issue could be that you just have a talkative cat since several breeds, like Siamese cats, are very verbal. The scratching is a different story. I would try playing with him using stick-like toys regularly. If he is fixed, I won't let him out anymore. Instead, give him a shelf near the window so he can look out if he wants. Sometimes, bird feeders and bird baths can provide hours of entertainment. Also, be sure you do not give him attention when he scratches. Instead, gently push him away from you and leave. While doing this, be sure to provide him with love and/or treats when he plays nicely with you, looks out the windows, and leaves areas when told (example would be the stove). He may also be afraid that you are going to leave without paying attention to him since he is a feral cat and experienced that often. Hopefully, his behavior will settle down over time.