I'd recommend using OGR/GDAL, which is part of the GDAL library. OGR supports a virtual format which allows specification via an XML file. If you convert your Excel worksheet into a CSV, you can generate a VRT to access the data.
Assuming you have something like this
34.0,-120.0,2010-05-01,Off Santa Rosa Island
You can create a VRT
example.vrt as follows:
<GeometryField encoding="PointFromColumns" x="Long" y="Lat"/>
Starting in GDAL 1.7, you can additionally specify the datatypes of attribute fields using the
<Field> element inside of
<OGRVRTLayer>, like so:
<Field name="date" src="Year" type="Date" />
Keep in mind that shapefiles store attributes in the DBASE IV format which has less flexibility in data types than Excel. Once you've got your VRT file specified, you can use the normal OGR toolchain to convert the data into a Shapefile:
ogr2ogr -f "ESRI Shapefile" example.shp example.vrt
Unfortunately, #4 is not possible — the shapefile specification allows a single projection (viewable here in
example.prj after the last step).