1) getting that huge 808 kick is a problem everyone runs into at some point- in my mind there are 3 things you need to do to get it.

1- pick the best 808 kick sample you can find. I'm not familiar with fls native sample packs, but you're looking for something with a long decay and a solid thud right at the bottom of the bass range. Sub bass range should be full too, but it doesn't matter as much because you're gonna want to eq the bottom out after 20 hz or so.

2- you should set whatever sampler you're using to a long decay so the sound "hangs around".

3- This is the most important part: processing. You're definitely going to need an eq or two and a compressor. The order you put them in is a matter of taste, but I usually eq>compress>eq. The first eq is to get the initial shape of the sound so compression is more focused. This means you need to set it to boost the high end slightly and roll off the inaudible sub bass. Excess subbass through compression muddles low end. For the compressor, you want it pretty gentle, but dial up to taste. You want to keep the initial attack of the drum while boosting the volume ofthe tail which means you need to set the compressions attack behind the thud of the kick( just a few ms) and the decay quick enough that the lower volume tail doesn't get crushed. The second eq is to boost the sweet spots (~180-220) and the high end and roll off the subbass again.

2)I'm in class so I can't listen to the track, but if I had to guess they're probably in part using a reversed reverb. Super simple and effective technique. You just record a sample going through a reverb and bump it to an audio track and reverse it. If you line it up correctly it sounds as if the sound is emerging from the background. Really great way to introduce new elements/introduce some swing