DSG is the Direct Shift Gearbox auto transmission that was
only offered on the 2004 NB TDI. You have the standard issue five speed tiptronic transmission in your 06.
VCDS (or VAG-COM as it was called) is the Volkswagen Computer Diagnostic Software from Ross-Tech that connects to your ECM through the OBDII port and can analyze many modules on the vehicle and point to problems and detect DTC's (defect trouble codes) when your check engine light comes on.
As far as doing the timing belt, water pump and tensioner service yourself, it is very doable but as Smileybug has mentioned, you need to have the proper tools to do the job. It is a bit easier on the BEW diesel's (which you have) and you DO NOT need VCDS to do it. But, without the proper tools it would be a bit of a challenge and the risk of not getting the camshaft locked and the crankshaft locked is too great when you consider that these engines are interference engines and just a few teeth off on a timing belt will grenade the valves into the pistons pretty quickly.
Now, as far as the hard starting is concerned, dirty fuel, air in the fuel line, a clogged egr valve, clogged intake manifold all will contribute to difficult starting. Glow plugs are only necessary for temperatures below 40F so if you are having difficulty starting in moderate temps, glow plugs won't help.
There are two things that will cause hard starting.
1. If you have a weak or failing engine speed sensor, located on the front bottom of the engine block, then it will absolutely prevent the engine from starting. It works in concert with the crankshaft position sensor but a faulty crankshaft sensor will still allow the engine to start. A bad engine speed sensor will not allow the engine to start under any circumstances.
2. A bad fuel lift pump in the fuel tank. The PD engines are different from the 2003 and earlier TDI's. Instead of having a tandem fuel pump in the engine bay, there is a lift pump in the fuel tank that runs momentarily when you turn the ignition on to prime the secondary fuel pump and build pressure in the system. If that pump fails, the engine will start but will take longer since it now has to rely on the secondary pump only to pull full through the fuel filter and deliver it to the individual high pressure pumps in each cylinder. You can check this by listening for the pump to run under the rear seat when you turn the ignition on. If you don't hear a short hum, then you have a bad lift pump and it will need to be replaced.
Kinda a long explanation here but hopefully you will have some insight on your issue and can better diagnose the problem. It sounds like you're fairly adept at this car stuff so it shouldn't be to difficult for ya.
Again, an excellent resource for all things TDI is to visit Freds TDI Club at
Fred's TDI Page. TDIClub.com. VW TDI Enthusiast Community for everything you ever wanted to know about VW diesels.
Hope this helps and good luck.