There is weirdness in the revised expansions, and more weirdness in the BGA implementation of it's sets. Every game will have the base set, plus any sets you choose to include. The community mostly adopted a "more is better" approach to adding cards in so most games have all of the sets on BGA, or as is the case currently there may not yet be wholesale adoption of the newest set with some games excluding it.
To go into the settings mentioned more specifically.
Competitive level: beginner is the family game, normal allows all cards in the chosen sets, competitive removes cards in the banlist from the chosen sets.
C&D Cards: It adds the C&D decks, but the only cards marked in the C&D set are from the Wizkids mini expansion. This has some very weird and I believe unintended behaviour. If you exclude C&D you won't get any C&D cards, even if they're in other sets.
New set of cards: This adds about half of the cards from among all of the A-D expansions. They are mostly the easier half to program, with some cards that were programmable being excluded due to advisement by a few strong players to the developers that such cards would likely be banned immediately.
Even more cards: This adds a lot of the rest of the cards in A-D expansions, plus the E deck. E deck is great, the cards that were excluded from New set of cards tend to be not great - some are complex effects that were hard to program, some cards really need to be banned.
If you are new to Agricola as a whole, the base game tends to have simpler cards that promote a more new-player friendly experience (the game can be about starvation more than farming if the table collectively mismanages it, and the revised base set gives you stuff to focus on that avoids this starvation problem), with the complexity going up a little bit with C&D and up again a lot with the New set.
