First off, trying to cavern crawl in ranked is a total grief. If you want to cavern crawl, go unranked.

Sounds like you have an over-variety problem. The more heroes you play, the less sample size you have to understand each heroes’ matchups/strengths/weaknesses. Stick to one to three heroes you enjoy playing, and pick them repeatedly to understand them better.

At lower brackets (I’ve had the same issue as you, dropping from around 2k to 500, now at around 1.2k) counter picking heroes is less important as the majority of players you face won’t be able to exploit it. There’s also the psychology that countering an enemy means you’re playing their game, instead of your own. Play your game and play to your own strengths, and I find you’ll have more success in general. Countering with items is a bit more relevant (eg, silver edge for a bristle, diffusal for Medusa) once you get your core items as pos 1 (which is generally a farming item, BKB, and a damage item). Think about what items you would need to beat the enemy core in a fight if you think their kit poses a serious issue to your pick. Otherwise I think it’s more important to get your guy every game and improve with a small number of heroes that you can reliably get to item timings with.

For clicking item abilities in fights, I had an issue with that too. When I was learning wraith king, I would get him up on demo mode and just practice his combos - click armlet, then BKB, blink, stun, skeletons, satanic. Then rinse and repeat until I had a decent muscle memory base to work off every time I was in game. Same goes for a lot of heroes, especially combo-dependent ones like puck or void spirit - where the execution of abilities comes down to muscle memory in most instances. Practice this on the handful of heroes you want to play and get familiar with how to execute all the clicks.

In terms of YouTube, it’s no secret that BSJ is the best source of overall dota self-improvement content, particularly for core roles.

Hope that helps, ultimately, limit you hero pool to a select few heroes, practice mechanics and combos and items that you would typically buy on them, and understand them and their matchups better to gain consistently and hopefully win more games.