In all honesty...there are good and bad everywhere. Yeah there are many tradespersons who don't give a fuck and there are those who do. The problems lies in how many people they tell and the type of people they tell. Do that shit yourself if it's not beyond your scope...there are many who will...
Making the final 45 degree cut under water works well...also, don't forget to mist the clones a once or twice a day for the first week or so as they have no roots and will absorb the water through the leaves. For the first time I'd recommend using soil or rapid rooters as mentioned...it's so easy.
PH is important regardless unless you're using pH balanced soil such as PROMIX. Also, drainage of the soil is equally important as you can easily accomplish this by adding 10% perlite to the mix. Over watering and over fertilizing is a very common problem when starting out so I would be very...
Flat white paint is much cheaper and has good reflectivity at about 85% of incident light. Mylar is more efficient at about 95% which would not necessarily be justified by the significantly greater cost.
I'm gonna agree with the lack of oxygen as the issue...when roots are submerged in water, you'll need sufficient aeration. The pump can be larger than the required size but not less.