People can give better advice if you have screenshots of your champion roster and champion stats. That way we can give you possible team comps for each dungeon and tell you what you need to improve on your team. :)

Some suggestions about your post. Lxzy can correct me if this is not a good idea.

• You might get better response if you focus your question on one dungeon at a time. 
• If you provide your current team for each dungeon, and what level dungeon you are on, suggestions can be made based on the difficulty and affinity of that boss vs your team.

Quick observations:

Apo can probably be on all of your teams at this point. Probably should be your next 6* champ.

So I need to focus on Spider at the moment. How do I clear level 20, which Champs I should work on and what gear should I use?

i think dragon 20 should be prioritized before working on spider team.  so zelotah, spider, apothecary and a poisoner

Not trying to dodge your question but there are many good u-tube videos on that subject by various commentators.  But my opinion is that the same champ is different for every person, and how it is geared.  Your M Monster will still be different than mine (if I had one), so might not produce the same result.

What I do to start with, is to look at the in-game reviews (or outside reviews if you have them) for the collective opinions (could be many hundreds) on each champ's performance in 14 different areas, such as arena, spider, dragon, keeps, clan boss, etc. I have made a spreadsheet of the ratings for all my champs, so I can sort them.  So if I want a clan boss team I sort my rankings and pick the top ones.  Possible that a champ may not be well developed yet so I skip to the next one.  That way I can come up with a starting team for each situation.  Over time the team can be tweaked based on trial and error, and some specific skills you may want to introduce into the mix.  Also when you have aura, you should try different champs as  your leader and see what scores best. Also may need to fine tune for force-magic-spirit-force effects.  I also take the average of all the ratings on all the champs to see which ones I would want to keep or get rid of.

I realize others' opinions are only that..opinions, so you have to make the final choices, but at least you have a place to start.  Teams may change, what you need for L10 Ice Golem might be different than for higher levels.  Artifacts are a never ending evolution, you will constantly get newer and better ones over time.  It costs silver to remove them, and then to upgrade ther new ones. There again, I use the ingame recommendations for the sets and attributes they suggest to get started. If the ones they suggest are not available to you, then judicial substitutions are needed.  Some sets have alternatives, like offense and cruel for example, or life and immortal, speed and divine speed, etc.

Just as a general observation on your champ listings, I notice many of them are not yet "ascended" to minimum Level 3.  Look at your Champs for those that would offer different abilities if "ascended", noted by an exclamation mark (!).  Level 3 is what is needed to activate additional abilities.  For example, a basic skill might be a 25% increase in ATK, but if ascended, that could be 50% increase.  The ascension info is shown in the skills section for each champ.  Even if special skills are not involved, ascension increases basic stats.

I agree with Trips, focusing on Dragon will help you progress better now, rather than Spider. Based on your roster, it doesn't look like you have a Spider 20 team yet. I may be wrong, others can help if you do. 

Eventually the champs you have now may not be used on Spider or Dragon 20 teams. You will change teams based on your needs and who you have available, like Lady mentions. 

I was only able to get past Spider 14 when I pulled M. Monster during the recent Halloween 10X event. Then I got Armiger to 60 (based on Trips advice) and he got me past Spider 19. Now I can auto Spider 20 with core team of Tyrant (HP Burn) and MM, then Armiger and Alure for turn meter reduction, and Scyl for healing and reviving of Armiger.

What is current Spider team and what level can you complete (auto/manual)? It gets a lot harder at lvl 13 or 14, so strategy needs to change.

What is current Dragon team and what level can you complete (auto/manual)? Earlier levels you can win by brute force, but later you may need to change to a poisoner as Trips suggests. 

Ultimate Galek might be very helpful for Spider, Dragon and CB team. Check out some YouTuber videos for building him. 

Thanks guys, I appreciate you guys taking the time out to explain the intricacies, I will check out the videos avaiale on the subject.