It seems obvious, but it bears repeating: there’s no quicker way to lose readers than by having a site that a) is too slow or b) doesn’t work (whether that be broken links or something more complicated like malfunctioning logins).
Web readers have a pretty limited attention span, unless they’re really, really looking for something specific. Think about it: How often has it happened that you’ve clicked on something interesting, waited about 10 seconds for it to load, given up and moved on? You may not have thought about it much at the time, but for the owner of that site, that was lost traffic.
The key is to not bite off more than you can chew. Know what you’re capable of and do it well. This isn’t to say you shouldn’t dream big – just make sure each step is implemented properly before moving on to the next.