This site lists the 2009 Giant TCX 2 as 10.2 kg (frame size not specified) but that is only 22.4 pounds Giant TCX 2 review - BikeRadar USA so adding a kickstand and fenders would not add 13 pounds to the bike. I just weighed an aluminum kickstand and it came to 230 grams which is half a pound. What you get as a trade off for just having one gear may come at the expense of your knees. I haven't had a one-speed bike since I was a preadolescent and there is no way I would go back to those days. The advantage of multi-speed bikes is the ability to choose a gear that is comfortable for the terrain. If you have only one gear, then you will be mashing up the hills and spinning like mad in other circumstances.

You can calculate the gear range (or single gear) here https://sheldonbrown.com/gear-calc.html
If you use the numbers you listed 11-28 cassette and 34-50 chainrings plus 700X38C tire, 170 mm crank you will get a gear range of 33.2 to 124.2 gear inches for your current bike and 18 gears to select from.