For a small venue, a 3500 to 4000 lumens projector should be sufficient, for a medium size venue, 5000 lumens is the most common. For a large venue, a 7000+ lumens projector is recommended.
Most common resolution is XGA, WXGA (HD in 16:10 format) and FULL HD (1080p). If only simple graphics and text is presented, XGA is sufficient. If the presentation material has a lot of fine detail, a FULL HD projector is recommended.