Looking for guides/tutorials that will help me with my mistakes (pictures included)

As you would appear to be new to watercolours, then I'm going to offer what might appear to be simple, perhaps even naive advice. Colour mixing/ tints/ shades is something that gets better the more you practise doing it; grab a few dollops of colour, a brush and water, and experiment. Looking at your painting of the rose, there's actually not a lot that's wrong with it. I'll leave brush care to those who work with brushes more than I do; the question must have come up here oodles of times.

A very quick response re weak mixes as I'm going out. The way I do it is to put a puddle of water in the mixing bowl and add just a little pigment (the wash). Then load your brush - no don't knock excess wash off the brush on the side of the palette - and paint with the loaded brush. You can always reduce any excess wash off the paper if necessary with a slightly damp brush which will soak it up. Hope that's clear - only one way of doing it but practice is the key. Quick edit - there are other ways to approach this of course one being to paint the paper with clear water and then mix the required colour and drop it into the water with the tip of the brush but not all over - this way you get some lovely graded results - must dash the cars waiting.

If that's your second watercolour, you have already made more progress than most watercolourists would have achieved by their tenth or twentieth. All you need to do is practise, on any scrap piece of watercolour paper you can find, until you're more confident in mixing colour. I should avoid white, other than in the most minute quantities - let the water grade the strength of your colour: there are various means of doing that, none is right or wrong - eg, you can mix your tones of colour in separate wells, you can apply the colour to damp paper, you can apply the colour and then drop water into it - and more. You will find your preferred methods - there's likely to be more than one which appeals to you - as you practise. Your brush is a little small for the size of painting you're working on - and yet you've still managed to get a good, clear wash with it: I would certainly have struggled with that.... When you can manage it, buy a few more brushes: say, a 3/4 inch flat, a round, and a rigger: you don't need many. (You don't need to pay a fortune for them, either: a good range can be obtained from Rosemary & Co - I think many of us would recommend them.) Cleaning your brushes - I really would not use isopropanol, especially if you're using natural hair brushes like sables: the chemical can leave the brush dry and lifeless. All watercolour brushes, whether made of sable hair, goat hair, or synthetic bristle, need is plain water, with perhaps a little plain household soap now and then. Some people also give their brushes a treatment with conditioner - the stuff that people use on their own hair - very occasionally. I doubt that it does any harm; it might do a little bit of good. But harsh chemicals and industrial alcohols should be avoided on the delicate filament of watercolour brushes. Make sure you rinse your brush out so that no soap remains in it: and never use hot water - bad for the hairs, and can loosen them in the ferrule of the brush. And keep painting - you've made a very impressive start.