With 1000 posts per day, I would suggest that you get 300 MB shared SQL server space and a shared web host. I recommend you go beyond regular shared hosting plans (I believe you are talking about 400 active users), and get a semi-dedicated host (where only a limited number of sites are hosted together). A good example would be the Semi-dedicated plan offered by webhost4life.com (basic package), or the VPS by maximumASP.
Actually, the software is very capable in terms of performance so it will never be the bottleneck of your site's performance under the load you specified, even on a very ordinary shared hosting plan (where more than 100-200 sites are hosted together), but with such plan you will experience a lot of problems caused by others, and with a community of your size you cannot take chances.