Having done this job like four times already on DQ250s, I will give just some quick advice as you've already got lots of threads on DIY/How-tos, etc. on the intarwebs. Here's another one for you, btw:
How to DIY change DSG transmission fluid and VAS6262 tool service on VW Jetta TDI
www.myturbodiesel.com
Firstly,
get a transmission pump with the proper fitting...or some kind of kit that fills by pumping from the bottom. Trying to "top fill" is silly, IMO. Takes too much time and if you plan on keeping the car long term (where you'd be doing this job more than once), might as well get a pump. Also going from the top means you'll want to poke holes in the bottles so the fluid can flow faster but then you can't reuse those bottles to take the old oil for disposal. This is not a hug deal if you have some other container to pour into but personally I'm usually using the new containers to put the old oil back into.
Secondly...
overfill it. I don't mean go nuts and put like 8L in there or anything like that, but worry more about underfilling than overfilling. The "correct" method is that you have to install the snorkel and pump fluid in, until you've pumped a full 5L. Then with it at temperature and running you pull the fill line and let it drain to the level of the snorkel. However if you do this, if you've done the "science experiment method" (where you measure what you drained out) you'll probably find that the net of what you put in was less than the car had originally. The actual amount in the gearbox will likely be more than 4.5L but less than 5L, if you measure what you drain out. But, then you have to account for what the filter soaks, plus you also have to have the car
level to do this and getting a car 100% level is easier said than done for a DIYer--for example is the surface you're working on level? Are you able to lift the whole car? Etc.
My best advice here is just overfill it, pump in all 5L, cap it and call it a day. This will usually require cracking the 6th bottle when you're using a pump because a lot of pumps don't "scavenge" all the way to the bottom. My Assenmacher pump for example, it really can't pump the last half litre or so in its container since the level is too low for the pump to pick up.
Again having done this job multiple times and having to later jack the car back up and pump more fluid back in a few days later...I've learned the easy way to do this is just "overfill it". Pump in a full 5L, maybe even a couple hundred ml more, and call it a day. Gearbox works absolutely fine being a little overfilled, but being a little underfilled...you're probably going to notice it's not shifting exactly how it should.