#1 Breathing:

I am concerned that you indicate there is more phlegm after feeding - feeding should not be increasing the production of mucus. Generally one would suction before feeding so as to decrease the risk of vomiting as stimulated by suctioning/coughing. I worry that aspiration is occurring during or after the feeding/
As for the length of suction - for a trach you would place about 1/2 the length of the suction cath into the trach. Once a cough results, you know you shouldn't go further. Try to insert the cath while the patient is breathing in - that's when the trachea is likely to be dilated, rather than constricted.
The saline instillation has been a standard since I graduated almost 35 years ago. Then there were some studies that said that the instillation of saline would drop the O2 sat. My response to that is, so don't do it on the patients who have a noticeable drop, but on the others maybe it's ok. Then a few years ago, there was a study (probably several) that said that instilling saline would result in the colonized organisms in the trach or ETT being washed down into the otherwise "sterile" lower airways. Our hospital has adopted this belief and we only use saline when absolutely necessary, rather than as a routine.
I am new here, hope to be on again soon.