I am sorry you are in a tough situation. Boots is a pretty boy and it is clear that you love him. Maybe you can find a way to make things work soon, but if you cannot, giving him to another loving home is not a defeat. There are other possible endings to this saga that would be worse for you both.
If you think you might ever 'spank' your cat again, find it another home and/or get it into a no-kill rescue as soon as possible. You cannot punish meowing or restlessness. If the spanking 'works' it is because he is too terrified afterwards to do anything at all. That is not acceptable. He was very scared during the entire time he was chased around as well as during/after the physical punishment.
In order to prevent any more physical punishment, be prepared to shut him in another room if his behavior is making you frustrated. Put his food and water and litter box in the bathroom or kitchen or laundry -- someplace where he can be safe and you can go back to sleep. Put him in there promptly when your frustration starts to rise, so that you don't wind up chasing him around the house. Turn on a radio or put in ear plugs if he continues to be loud. Stay away from him when you are very frustrated.
As for the 5 day trip: Even if you did leave ample food and water, if you did not have someone drop by to check on him and spend a little time daily, then I think it is not surprising that he experienced this as abandonment and is now experiencing separation anxiety. I know that a lot of people expect this to be fine with their cats and sometimes it is, but I know that mine were very upset with me when I was gone for a week even though I had friends who would spend an hour or so at my place each evening to take care of chores and hang out with them.
If you want to heal this situation, then IMHO, you will have to look into your own heart and change how you have been relating to him lately. Do you play with him - roll the ball or play with a toy on a string? It doesn't cost money, but it does take time. If you can't have a second cat for him to play with, then you have to be his playmate. Do you want to do that? For a half-hour in the morning? And again after you get home from work? And before bed? Do you brush him often - have plenty of gentle physical contact? Are you home 2-3 hours most evenings before you go to bed (or 2-3 hours each morning before you have to go to work)?
As for more toys for him -- grocery bags left open on the floor are free - expect a big mess! Leaving a kitchen cabinet empty and propped open so he can play hide and seek is good. Make sure all the windows have furniture beneath them that he can climb and look out. Other free toys: Lids and rings from plastic milk jugs (so long as he doesn't eat them). Your old socks - make sure the new ones are kept put away so he doesn't confuse his toys with your clothes. Stuffed animals from Salvation Army or Goodwill are a dollar and he can carry them around, attack them, rip them up and pull out the stuffing (make sure he is the kind of a guy who won't eat it before you leave him alone with his prey/friend).
The Feliway suggested above is good stuff -- so is Rescue Remedy and/or other Bach's Flower Essences <
http://www.bachflower.com/Pets.htm>. Pick one you think might work best, they should all be available at your local health food store/co-op for about $12.00.
Rescue Remedy: This combination of 5 Essences is a "must have" for all pet owners. It is excellent when taking the pet to the vet, after a trauma, when the pet is "not quiet well," or after an accident.
Chicory: For a pet that is in constant need of attention.
Star of Bethlehem: For an animal that have been through a traumatic experience, such as, attacked by another animal, been lost, being abused, moved to a new place, lost a loved person, been in an accident or other traumatic experiences.
Vervain: For animals that is hyperactive and always on the run.
Walnut: When changes are happening or when there need to be a change in habits. This Essence help the pet adjust to a new environment, new people or any other situation where there is a change or a need for a change. This Essences can also help a pet that is being affected by their humans emotions, Walnut protects the pet from our negative emotions.