tronbomb

I'm a newbie to the forum and have really enjoyed reading up on many of the posts. I have a mysterious one. I have a 2000 Maxima GLE with almost 150,000 miles on it. A few months back it was running kind of rough, so I gave it a tune-up and replaced two of the coils. Recently on my way to work, my check engine light, ABS, TCS, etc all came on and then all of my gauges started to fluctuate. I pulled the car over and shut it off, and then it wouldn't start. I am in no way an expert mechanic, but I can do the basics. I assumed it was probably just the battery as it is the original battery. Put the new battery in and it ran just fine, for a while. A few days later it started doing the same thing, so I came to the conclusion that it was the alternator and not the battery. I took the alternator out, had it rebuilt put it back in and it started right up and it has been running fine for the past week or so, except for the fact that it starts real hard sometimes. Before I started having problems it started right away, every time. Sometimes it takes about 10-20 seconds for it to start, the next time I go out to start it, let's say 15-30 minutes after it has been sitting, it will start right away. There really doesn't seem to be a pattern, sometimes it starts right up other times it takes a while. What could this be? Once it is started, it runs like a dream. Could the starter be getting weak due to the extra abuse it has been taking with my other electrical problems? Any ideas or suggestions would be greatly appreciated.