Using full flash, as in flash-on-camera, does not give a 'portrait', though it should stop any movement blur.  The best aperture of most lenses is somewhere around the middle of that lens' aperture range, but high-max-aperture lenses, e.g. f1.4, tend to have best sharpness close to that max aperture.

Focus carefully for max natural sharpness. Indeed use low ISO, which is what I think you mean by '100-grain' - your expression has no meaning.

Use some sharpening in your image software, but not too much.  Always work on a copy file!

And remember that working digitally allows you to experiment at no cost.

Note to Sumi: f11 is a small aperture, f2 is a large aperture.

Getting details is mostly about lighting. The stronger light you use, the easier you can emphasize shadows which in effect brings out more details. It's not just the amount of light. It's positioning so experiment around with angle and distance.

It is unlikely that the lens setting i.e. f-stop will play a dominate part. This is because most lenses will function well when the image is shown of a computer screen. However, the sharpest f-number setting is about 2 f-stops down from maximum opening. Generally this will be about f/8. 

To show texture is all about lighting. You will need a minimum of two lights for this gig. You can use pin-up flood lamps from the hardware store. Your digital camera’s white balance will handle the color output of these store bought lamps.For texture enhancement, set one lamp high and slightly off to the side. Measure the distance lamp to subject in inches or centimeters. Multiply this distance by 2. Place the second lamp at lens height as close to a line drawn, camera-to-subject. It’s distance from the subject is 2x compared to the other lamp. The high lamp is called the main, the low lamp is called the fill. It is the difference in distance between the lamps that emphasizes texture. You can increase the illusion of texture by moving the low lamp further back. Try placing it 3X further back th an the main. These distances assume both lamps are equal as to brightness. Exposure setting is based on illuminating the subject with the low light. So, turn off the main, with fill only, take an exposure reading. Set the camera on manual. Turn back on the main and expose using fill only reading.What is happening is: Main cast shadows. The fill is subordinate to the main. It softens the shadows. Its placement determines the contrast of the resulting image. 2:1 ratio (flat light) main and fill equal distant. 3:1 ratio fill is 1.4X further back. This studio standard. More contrast and texture, fill is set 2X further back 5:1 ratio. Set the fill back 2.8X = 9:1 ratio very contrasty.Don’t knock it till you try it. Focus on the eyes. Remember to keep the main high to simulate afternoon sun. Remember the fill is at lens height. Keep other lights away so they don’t spoil this effect.

Use the lowest ISO setting on your camera because it'll produce the least amount noise, the sharpest results and the best color & contrast.

You do not want to use f/11 as this is 1) too large of an f/stop producing too much depth of field, and 2) it's usually not the sharpest aperture of any lens. 

The best aperture varies but it's usually one or two stops closed from the maxiumum aperture.  However, if you're using a lens with a max aperture of f/5.6, then you'd be at f/8 or f/11 which is likely to produce too much depth of field.  In this case, you'd rather sacrifice a little sharpness for a better blurred out background. 

Portraits aren't usually made with the sharpest lenses because no one wants to be able to count the blackheads on their nose in the shot.  It's therefore common to use a diffusion filter like a Tiffen FX-3 or Pro-Mist.

Use flash to add a catch light in the eyes and if you're outside, the flash will fill in any deep shadows.  However, the best way to use the flash is to take it off the camera and off to the side. 

If you have the subject lit from the side, the light will produce more texture as it rakes across the surfaces in the frame.  However, again, this could cause there to be too much detail and texture for a portrait.

Use a good lens for portraits.  Avoid short focal lengths below 85mm.  Preferably anything between 85-150mm is a good portrait lens.  50mm lenses on an APS-C camera are okay since it has an equivalent angle of view to about an 80mm, but they do not compress the perspective like a real 80mm.  For this reason, use a long focal length to compress the perspective which makes your subjects look more attractive than they normally do in real life.

You need a sharp lens. Most lenses are sharpest at around f/5.6 to f/8, when most lens aberrations are well corrected, while diffraction does not yet become a factor in reducing sharpness. A 90-100mm macro lens would be ideal if you want the sharpest portraits. Women generally do not like sharp portraits because they show all the flaws on their skin. 

Super sharpness and texture are difficult to achieve at the same time, and very often having the background also in sharp focus fails to separate the model from it. Busy backgrounds are not ideal, but fence panels with repetitive patterns when blurred can still work OK.  Focus on the model's eyes and light meter for the face. Use 50mm equivalent focal length (37mm on an APS-C sensor camera) for the most natural look or 80mm (55mm) for a more flattering look, If you want texture make sure you have a nice element of side-lighting but not too harsh. Also have the model wear things with different textures and have interesting hair. For maximum potential sharpness in well lit conditions stop down to between f8 and f11. For a natural look try f5.6. For max depth of field use f16. It is very much a learning game, none of it is easy at first.