Did I do anything to mess myself up, or am I just being paranoid?

I was told that I would be offered a job on Monday, and received the offer letter via email on Thursday. He brought up the salary issue first during the interview, and I indicated that I was hoping to get $5k more, but I thought that the amount he was offering was reasonable and that I would consider it and was willing to be flexible.

I spoke to him on Thursday after receiving the offer (the amount he mentioned at the interview), with some questions related to issues not mentioned in the offer letter or that were unclear. I didn't discuss anything about the salary, and said I would return the signed offer letter either later that evening or on Friday.

I've been unemployed for quite a while, and my future employer is aware of this and knows I'm in no position to make demands. While the offer is withing the realm of reasonableness, it is on the low end of the pay scale. My initial plan was to just sign it and take the job, but after speaking to my brother, he thought it would be reasonable to request an initial 6 month review prior to the annual review. I was also thinking maybe I could see if he had any flexibility and could up his offer a little bit, or perhaps instead offer an extra week of vacation (it is only 2 weeks). I don't want to risk losing the offer under the circumstances, but I thought that it couldn't hurt to ask politely rather than making it adversarial, and accept the job no matter what.

I called Friday afternoon (on his cell phone, which is the only number I have) and said that I was ready to send him the offer letter, but I just had a few more questions first. After not being called back by the end of the work day, I emailed him back essentially saying the same thing. I said that I'm not trying to hold up the process, and I would send back the offer letter as soon as I was able to ask him a few more brief questions. In the email, I said that I did not want to call and disturb him over the weekend, but that he could call me, otherwise, we could talk on Monday.

I want to make sure that I didn't do anything to mess myself up. He had to interrupt the call on Thursday, and he told me that his grandfather was having surgery, so I'm wondering if perhaps it had anything to do with that.

One friend suggested that I just email back the signed offer letter now, and negotiate after the fact. However, I don't think this is really possible, although I don't expect to be able to get any more, and the review period isn't in the offer letter to begin with, so conceivably I could ask after the fact.

This offer is $1k less than my last job, but I'd be expected to put in a lot more hours. If I still had my last job, I wouldn't take this one unless it was $15k higher, and wouldn't be concerned about making demands and causing the offer to be revoked. But I'm very panicky and want to make sure I get this, even if things are not nearly as good as I'd like.