1. Yes you can dose dry ferts, it's pretty easy if you follow EI dosing for low tech tanks. Here's the calculator I use for all of my tanks http://calc.petalphile.com/
you just enter how many gallons your tank is, select us gallons, click DIY, select which fert you're dosing, select dry dosing, then select EI low light/weekly and it gives you the amount to dose into your tank, and you can just dose the ferts dry right into the tank.
I use a digital milligram/gram/ounce scale to measure out the exact amount of each fert, so I would recommend getting one. So because you'll be following EI dosing for low tech, it means you'll only be dosing your tank once a week.
I have a 45 gallon long high tech tank so I use EI dosing weekly schedule like this
Mon/Weds/Fri - Macro's (potassium nitrate KNO3/monopotassium phosphate KH2PO4/Potassium sulfate K2SO4)
Tues/Thurs/Sat - Micro's Plantex CSM+B
Sun - 50% water change
2. Co2 will depend on how much lighting you intend to have on the tank, example - I have a 45 gallon long tank (48" x 13" x 19") with a T5HO quad lighting system which means I'm forced to have co2 because of the high lighting. With a low tech set up there's really not a need for a co2 injection system, and you can dose flourish excel which is a liquid carbon supplement for plants and replaces the need for a co2 injection system on a low tech tank.
3. Diatoms are very common in new tanks, and tend to go away after a few weeks as the tank matures. Also Otocinclus algae eaters love diatoms...