Hey there, I just subbed your channel. I'm not saying my channel is of any quality, or that I'm in a position of authority to offer advice, but you're asking, so I figure I can answer, from the perspective of someone with ~80k subs currently:
First thing I did was say "cool look!" then I clicked 'about' link to learn more about your channel and ways that I could follow your twitter, etc, and there was not anything beyond a succinct description. I'm not complaining, and I doubt it will cost you much, but people don't want to have to work hard to follow your content stream, and it's like a set-it-and-forget-it way to wring out every last potential subscriber.
Your video production during your two book reviews was good, and your review was entertaining, personal, and seemed like an honest unscripted opinion. You have a great quality that you speak clearly and with intention; I appreciated that.
Your third video 'Designing Success' was in my opinion the best, design-wise :) (get it? design--... wise?) I liked the intro with the hip hop music and the artistic approach to conveying your surroundings and setting for the video.
The audio- I didn't mind the audio in the 3rd video when it got messy during the windy part, and I could see that you somewhat realized you were in choppy waters when the wind started blowing. You spoke clearly, and even as an American, accustomed to primarily listening to American dialect, I could still understand you- but one thing lacking that would have made it better was a proper Closed Caption track so that you could still be understood. That's just me nit-picking though, as someone who is hard of hearing.
An unsolicited tip: One thing I realized early on, making videos, is that you can't ever have too many audio sources recording. Audio recorders are cheap, and the mics you can attach to them are endless, so it's no issue to run several mics: one source could be the camera's audio, which I typically use for reference. Another option could be a portable audio recorder. Currently I use the Zoom H1, which was about 89 USD brand new. It allows me to pop in my headphones and monitor the audio as it is produced, in stereo, and if need be to connect something like a shirt mic, there is a port for that as well. One thing that I've been experimenting with recently, is if I'm recording outside, I'll also mic the ambient noise about 12 feet away and use that audio track to train an Audacity plugin to filter out errant jarring noises in incidences where loud vehicles or sirens drive past.
Great channel, I subbed, and look forward to new content. Take care! Good luck!
Also, if you haven't seen it already, check out the YouTube Creator Academy (formerly, the YouTube Playbook) which is pretty much a guide entitled "this is how to make money properly on our platform"
edit: corrected Zoom H2 to Zoom H1