Planning New Site With Newsletters

I'm planning a new site. If everything goes ok, with the offline promotion it will have, I'm sure it will have thousands of people registered during this year. I think at first I'll have a good hosting or shared server to see how it works there.

My problem is to find a good solution to deliver weekly newsletters to the registered users. I'm looking for a solution that can work where the site is hosted, but I find that almost all the hosting have limits on mail sending (example, 200 mails per hour) and I would like that the registered users receive the mails in just a few hours as max time.

Today I found this script http://activecampaign.com/12all/ and I don't know if it would help me. I think yes, but the limit on the hosting will still be there. What happens if I get a shared server? Will I still have problems with emails or I would have more liberty?

I also saw those solutions that offers other enterprises to solve the emails problem (like Sitepoint uses for newsletters). One of them is Constant Contact.

I would like a solution from the beginning that works no matter how big became my database of registered users.

All of this also make me wonder if I should plan the site using .NET or PHP (for example, if I consider a solution from another enterprise to send newsletters, it would be the same maybe, but if not, I should consider a script solution compatible with each platform).

I also wonder, how do all medium to medium-big sites send their newsletters almost instantly? (For example, if you have to send important news that needs to reach all the users in time, no 6 hours later because of mail limits, how they do that? If I have a shared server or my own server I would still have the problem of emails limit?)

I wrote some time ago to an enterprise of marketing email, and they told (don't know if it is true) that they have agreements with other enterprises to avoid detect their mails as spam.