Yes that was a long post :-D . About your situation there are some points I'ld like to say:
1- Are you sure that the domain name is not a trademark. A trademark is not simply the presence of a record in the US patents office. If he can prove that he advertised the domain name and it was linked to his business, then he has trademark rights. If he has trademark rights, then he can get the domain from you even if he left it to expire and you got it after that.
2- Network Solutions, "Hotmail.com" or anyone else can't do anything about the domain name. If he wants to dispute the domain name, he must first submit it to ICCAN through on of the Arbitration Services (the most popular is the National Arbitration Forum at www.arb-forum.com). Filing a complaint to ICCAN will cost him $1500. Then the NAF will ask the registry to put the domain on hold till it looks in the case. After he presents his case and any supporting evidences, the NAF will contact you by mail and email and set a deadline for you reply (usually 3-4 weeks). After they view the case, they either decide that the domain shall be transfered to Bob or not (if they decided to transfer the domain to Bob, Bob will be required to sent Network Solutions a copy of the decision. Network Solutions will wait 10 days before transfer the domain in case you decided to go to the court to dispute the NAF decision). If any of the sides didn't like the decision, then they can then go to court (most of the time the courts support NAF decisions). That will cost him a lot more!.
3- ICCAN has a standard Uniform Domain Name Dispute Resolution Policy (UDRP) at http://www.arb-forum.com/domains/UDRP/index.asp . Take a good look at it. There are 3 things that he must prove in order to get the domain from you. First one is that the domain name is similar or identical to his trademark. Second one is that you don't have any intrest in the domain (in your case, you have to prove that you are using the domain by having a website at the domain name or at least using it for emails, or designing a logo, or submitting a business plan,...etc). Thrid point is that you registered and is using the domain in "bad faith". Bad faith means you registered it to either harm his business or to resell it to him. He can prove the third point since you sent him an email saying that you'll sell him the domain for $3000. That was a mistake from your part, but remember he has to prove the 3 points otherwise the domain will be yours.
4- Contacting "Hotmail.com" is just an attempt to put pressure on you. Don't give it any thought.
5- the screenshots of WHOIS is not an evidence since they can be easily forged. However, Network Solutions or whoever is his registrar of the domains must keep a record of 3 months of changes to any domain. So they can prove what was his whois data and what he changed it to. It will not harm to keep the screenshots and submitting them to NAF if it got to there.
Good luck and let's know how it goes ;-)