Field size options missing from Name field (first & last)

Nothing is missing. There isn't an option to change the size on the 'grouped' advanced field like the name field. If you want to change those, you would need to target the inputs directly via CSS to manipulate the widths.

Sure. I forgot to include this earlier. See the section on "advanced fields" for how to properly target the individual inputs in the advanced groupings.

http://www.gravityhelp.com/documentation/page/CSS_Targeting_Samples

my telephone input field is set to type="text" and not to "tel" so direct css selection doesn't work as described.

The telephone field is a "text" input unless you turn on the "output HTML5" option in the form settings. The "tel" field is an HTML5 field.

http://www.gravityhelp.com/documentation/page/Settings_Page

email has the option small, medium, large but telephone doesn't (both special ungrouped)

The telephone field doesn't have a width option because the content is constrained/filtered to a standard amount of numerical characters. A longer or shorter input option isn't needed.

the medium setting leaves the fields to be wider than the single fields in the "grouped" fields

The field widths are variable (percentage based) so there may be some inconsistencies based on the available horizontal form area, other inherited theme styles, etc. While we try to make everything work as well as we can in most environments, there are times when some minor tweaks are going to be necessary due to all the variances in how themes are structured and theme styles are implemented.

You can use some more specific CSS rules to change the width percentage on the medium class if you need to adjust the alignment in your theme. There are samples of how to properly target form elements for CSS manipulation in the documentation here:

http://www.gravityhelp.com/documentation/page/CSS_Targeting_Samples