I can only reiterate what Martin and Omar said.
Going at a project on your own will be tough in the beginning. The guiding hand is just not there anymore. Completely normal and it will get better with time and practice.
Your workflow in general is good, never hurts to have backup where the modifiers haven’t been applied yet, so you can go back, when something goes wrong.
Like SubD on booleans for example. Martin said it pretty clear: SubD and N-Gons don’t go well together and Booleans tend to create N-Gons for a living. So it either takes a lot of clean-up to get as close to perfect quad topology as possible, or manual modeling to have more control over everything.
