An average timeline for angel investiments is 5+ years.
There are all sorts of Angel Networks. Most networks focus on a particular region and some specialize in an industry.
Different Angel Networks have different requirements to be an investor. Angel investors will spread their investments around several ventures at a time, since most will fail and a couple will provide a large return. $25,000 or $50,000 would be typicall investment that an invididual Angel contributes to a single venture.
Tax liabilities you should go over with your accountant, which you should be using if your doing these type of investments.