Change steps of logarithmic scale in PGFPlots and remove markers for selected series

Question

1) So I want my x axis' step size to be increased since it looks very cluttered as it is right now. Unfortunately it's a loglog plot so the usual

xtick={-5,0,5},

doesn't work. At the moment, it looks like this (the main thing inside the chart is omitted for privacy).

My MWE would be this but I guess it won't work without the data file itself which I can provide if needed but I think it's pretty straightforward.

\documentclass[letterpaper,12pt]{article}
\usepackage[margin=0.5 in,landscape]{geometry}
\usepackage[justification=centering]{caption}
\usepackage[dvipsnames]{xcolor}
\usepackage{pgfplotstable,pgfplots}
%\renewcommand{\familydefault}{\sfdefault}
\usepackage{mathptmx}
%\usepackage{sansmath} % Enables turning on sans-serif math mode, and using other environments
%\sansmath % Enable sans-serif math for rest of document
%\usepackage[math]{blindtext}
\pagestyle{empty}
\pgfplotsset
{
    compat = newest,
    every axis/.append style={semithick},
    major tick length=7pt,
    minor tick length=3pt,
    tick style={semithick,black},
    width= \textwidth,
    height= \textheight
}
\pgfplotstableread[col sep = comma]{dat.csv}\mydata

\begin{document}
\begin{figure}
    \begin{tikzpicture}
    \begin{loglogaxis}[
    xlabel=Re,
    ylabel=Fanning friction factor \textit{f},
    %y label style={rotate=-90},
    legend pos=south west,
    legend columns=1,
    legend style={draw=none}
    %no markers
    ]
    ‎\addplot table [y=fexpSS, x=ReSS, mark=only marks]{\mydata};‎
    ‎\addlegendentry{SS Experimental}
    \addplot table [y=fchurchSS, x=ReSS, mark=none]{\mydata};‎
    ‎\addlegendentry{SS Churchill}‎
    ‎\addplot table [y=fexpGalv., x=ReGalv., only marks]{\mydata};‎
    ‎\addlegendentry{Galv. Exp}‎
    ‎\addplot table [y=fchurchGalv., x=ReGalv., mark=none]{\mydata};‎
    ‎\addlegendentry{Galv. Churchill}‎
    ‎\addplot table [y=fexpCu, x=ReCu, only marks]{\mydata};‎
    ‎\addlegendentry{Cu Exp}
    ‎\addplot table [y=fchurchCu, x=ReCu, mark=none]{\mydata};‎
    ‎\addlegendentry{Cu Churchill}‎
    ‎\addplot table [y=fexpPVC, x=RePVC, only marks]{\mydata};‎
    ‎\addlegendentry{PVC Exp}
    ‎\addplot table [y=fchurchPVC, x=RePVC, mark=none]{\mydata};‎
    ‎\addlegendentry{PVC Churchill}‎
    ‎\addplot table [y=blasius, x=RePVC, mark=none]{\mydata};‎
    ‎\addlegendentry{Blasius Equation}‎
    \end{loglogaxis}
    \end{tikzpicture}
    \caption{Friction factors versus Reynolds Number for different pipes}
\end{figure}

\end{document}

By the way I would like to control the steps and min/max for my y axis too.

The CSV file can be downloaded here: https://1drv.ms/u/s!AnPuH_uDwkPFgo58-JfHJHs4CE4c6w

2) I would also like to remove the markers from the legend for the series where I have lines (i.e. the 8 series with lines drawn through the points) and would like the lines to be removed from the legend for the 4 series which have only points and no lines. I tried the solution here but it removed all the markers so it's not feasible. Something like what I did in Excel would be fine for example shown below.

3) I want to put a comma before the f here but if I do, it fails to load. Anyone has any ideas?

ylabel=Fanning friction factor \textit{f},

Answer 1

For 1) you can use e.g. xtickten + some extra x ticks.
For 2) you almost did it right. You just have to give the "mark" options to the optional argument of \addplot and not to the optional argument of table.
For 3) you just have to surround the label by curly brackets so the comma isn't misinterpreted as separator for the options.

Then I did some more small changes. For that, have a look at the comments in the code.

(The remaining issue now is, that the "Cu Churchill" line is laying almost completely behind the "PVC Churchill" line. This could be avoided e.g. by moving the dashed to the "PVC Churchill" or by using dashed and dotted lines for the last two lines.)

% used PGFPlots v1.14
% (the data file must be downloaded from the link in the question
%  <http://tex.stackexchange.com/q/337900>)
\documentclass[letterpaper,12pt]{article}
\usepackage[margin=0.5 in,landscape]{geometry}
\usepackage{pgfplots,pgfplotstable}
    \usetikzlibrary{pgfplots.colorbrewer}
    \pgfplotsset{
        compat=1.3,
        every axis/.append style={semithick},
        major tick length=7pt,
        minor tick length=3pt,
        tick style={semithick,black},
        width=\textwidth,
        height=\textheight,
    }
\begin{document}
        \pagestyle{empty}
    \begin{figure}
        \begin{tikzpicture}
                \pgfplotstableread[col sep=comma]{dat.csv}\mydata
            \begin{loglogaxis}[
                % put `xlabel' in math mode because "Re" is a variable
                % (same for "f" in `ylabel')
                xlabel=$Re$,
                % to use a comma inside the label, surround the label in brackets
                % so the comma isn't misinterpreted being an option separator
                ylabel={Fanning friction factor, $f$},
                legend pos=south west,
                legend columns=1,
                legend style={draw=none},
                % added min and max values to know where to put the extra tick labels
                xmin=9e3,
                xmax=8e4,
                ymin=4e-3,
                ymax=1.2e-2,
                % added (main) ticks
                xtickten={4,5},
                ytickten={-3,-2,-1},
                % added extra ticks at the ends of the axes
                extra x ticks={9e3,8e4},
                extra y ticks={4e-3,1.2e-2},
                % use ColorBrewer cycle list
                cycle list/Set1-4,
            ]
                % moved "mark" options to the optional argument of `\addplot'
                % and added colors manually, so they match for the same "set"
                ‎\addplot+ [only marks,Set1-A] table [x=ReSS,y=fexpSS]          {\mydata};‎
                \addplot+ [mark=none,Set1-A]  table [x=ReSS,y=fchurchSS]       {\mydata};‎
                ‎\addplot+ [only marks,Set1-B] table [x=ReGalv.,y=fexpGalv.]    {\mydata};‎
                ‎\addplot+ [mark=none,Set1-B]  table [x=ReGalv.,y=fchurchGalv.] {\mydata};‎
                ‎\addplot+ [only marks,Set1-C] table [x=ReCu,y=fexpCu]          {\mydata};‎
                ‎\addplot+ [mark=none,Set1-C]  table [x=ReCu,y=fchurchCu]       {\mydata};‎
                ‎\addplot+ [only marks,Set1-D] table [x=RePVC,y=fexpPVC]        {\mydata};‎
                ‎\addplot+ [mark=none,Set1-D]  table [x=RePVC,y=fchurchPVC]     {\mydata};‎
                ‎\addplot+ [mark=none,Set1-D,dashed]  table [x=RePVC,y=blasius] {\mydata};‎

                % moved legend here because (I think) it is much more clearly arranged
                \legend{
                    SS Experimental,
                    SS Churchill,‎
                    Galv. Exp,‎
                    Galv. Churchill,‎
                    Cu Exp,
                    Cu Churchill,‎
                    PVC Exp,
                    PVC Churchill,‎
                    Blasius Equation,
                }‎
            \end{loglogaxis}
        \end{tikzpicture}
        \caption{Friction factors versus Reynolds Number for different pipes}
    \end{figure}
\end{document}