Hi,
at first: Welcome to the board.
The renown points are measured by a few things. I don't know whether the total patrol tonnage counts or every ship for itself, which would include it's type.
Some things you get renown for are:
- sinking enemy ships
- reaching your patrol area
- patrolling your patrol area (for 24h)
- docking your boat at your home base, which means that you have to get into a
30km radius of this base and end your patrol there (It's more fun to get your boat
into the dock/bunker yourself though

)
But you can also lose renown for sinking neutral or friendly

ships for example.
Your other question:
You should definitely patch the game up to version 1.4b. After doing that there are many cool and free mods you can download and use.
GWX would be a good start

. It makes a whole new (and better) game out of SH3.
The "6_dials_nygm22" mod is really stylish and practical too, wouldn't miss that one.
At best you look into the mods section of the board.
So far, have fun
EDIT: Too slow :> The difficulty settings are quite important to the renown earned though.