They're really not all that hard to make on your own. One thing I like to do is export a sound I'm using in a tune and then run it through Paulstretch and clip a little bit of the resulting sound out to use as a transition. It can make some really cool atmospheric sweeps if you do it right. Another thing to try is to play with pitch bends and LFO speed automation.

Either. I make my own sub sweeps and white noise risers/falls layered with a cymbal or kick. Depends on the production and what I want to achieve. You can use a pad or a distant lead and automate the pitch, add some reverb and a whole lot of other effects like a phaser and just play around with it.

Valhalla shimmer + Edison for the best atmospheric stuff ever.

I like using the Granulator Max for Live plugin instrument for anything really atmospheric. Metallic sounds and vocals are pad city.

ValhallaFreqEcho for the win. You can do some math with http://www.seventhstring.com/resources/notefrequencies.html to figure out how many hertz to change with each echo to reach an octave in 4 bars, 8, whatever.

scraps. scraps scraps scraps scraps and more scraps.

Scraps are literally any sample which you slapped as many effects on as possible and twisted in different ways; reverb, phase, delay, chorus, granulation, more verb, pitch automation, etc.. go wild with the reverb. Seriously, go to town.  Make those suckers 3 minutes long.  Put a spectrum analyzer on it to check the key, save it with the key for future reference. 

I use these for dark atmosphere or even I'll even shape them further in my techno tracks to make trippy vocal shots. The idea is to overtime build a library of these things so that way you just have a whole bunch of different sounds to choose from which you can further shape to better fit the style of your music

I could never fathom using a sample pack for sweeps and impacts. First of all, they sound out of place unless you build the song around them.

Impacts - it all depends on if it's a naked impact (nothing else going on), you can drop a huge bomb here, but if it's placed in the middle of a mix you aren't going to hear the full effect unless you clear out some space. And it all depends on what's going on around it or where it is in the song, because sometimes a tom drenched in reverb is more appropriate than a kick, sometimes percussion does the trick when all else fails. The standard is using a kick from your track and using a huge hall setting with 50-100% wet, adjusted to taste. The tail could be timed to the track (60,000/BPM for quarter notes), this allows you to have the tail trail off appropriately according to the number of measures or bars you need it to. Or sometimes you just go by ear and bounce down to audio and then time-stretch that shit, which can be an effect in its own right. Man I could go on for days. Don't be afraid to layers well. One thing to note is that if you stack reverbs on top of one another it can get messy, even with surgical eq'ing, so best to try and group them all to a bus and apply reverb there, but again I suggest you experiment.

Sweeps - white noise is pretty standard. You can sweep the frequencies through it using a band pass, bounce it to audio and modulate the pitch. Do a combination of both, or whatever you want to do. If you can do elementary synthesis you can program a pitch riser in damn near any synth. Once you get better at it the sky is the limit, including looping vocals and making the pitch rise, or increasing the cut off filter on a plucky synth. Could go on for days

All in all I would suggest you critically listen to tracks you love and try and figure out what the supporting rise/impact/downlifter elements are, why they are there, and what role they have. Trying to imitate is always the best way. The most organic way to make these sounds is using elements already present in the track but if you can manipulate a sample pack to work, all power to you. I just find that they are drenched in reverb that may or may not be in line with your track. That's my gripe with most sample packs actually (zenhiser, vandalism, vengance). Or maybe I'm just a control freak.