I'll PM you with some of my recommendations,

but in short, there's no problem running 5 sites off of the same server. there's some SEO value to having sites on different servers but it's not all that important.

Yes it makes sense to use one host and one server for 5 blogs in the beginning you're traffic will not be a strain on your hosting. By the time it becomes an issue you will be able to move on to a virtual or dedicated server. There is only one hosting company I will use and a lot of people will tell you the same thing. Hostgator is the best for what you pay. Do a search for hostgator there are too many features to go into here again.

Make it easy on yourself and put it all on one server. A Hostgator shared account will be fine. There is no benefit to over complicating this step.

All that sounds fine. I use Godaddy for domains and Hostgator for hosting.

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Domain provider cannot provide you separate IP, your hosting provider can provide you different IPs.

No need to buy separate IPs for each niche, as your sites are in different niche, so I think there is no need of separate IP for each niche.

I agree with gittar1122 that there really isn't a need for separate IPs. The only reason would be if you were doing a lot of interlinking between these 5 sites and expecting some kind of SEO value out of it. Otherwise having 5 sites on 1 IP address is no problem at all.

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Applied Innovations - Windows Hosting, Windows VPS Hosting and Dedicated Servers sounds like it's right up your alley. We use them for most of our public facing sites. I also use 1and1.