GGTB is a very good choice, it has a quality look and feel and the purely mechanical operation is
flawless.
I found LR 901 atties give very nice vapour and flavour @ 3.7v (im not a fan of 6v
vaping so YMMV) im sure most LR atties / cartos would give similar results although i mainly use standard 808 cartos for simplicity while at work (plus the lower vapour production means less raised eyebrows and negative comments from management)

, a standard size 808 lasts me pretty much all day as long as im not caning it and a 17670 cell lasts well over a day.
When at home and feeling the need for a change of flavour (my GGTS AVS
tank is usually filled with RY4) i change the 808 for an LR 901 with a drip tip and vapour production is fantastic. I really like the simple design and versatility of the GGTB there is little to go wrong and if it does will likely be easy to fix due to the simple nature of the design and of course help is close at hand as these forums are very active with a lot of helpful and knowledgeable folks.
EDIT:- the KR808 - 501 adapter should work fine although the draw may possibly be a bit lighter depending on the adapter design.