The simple answer is, you shouldn't be worrying about what to leave out or retain, because you shouldn't be worrying awkwardness if your employer finds out, because your employer should know up front, because you have a responsibility to disclose this to them.
Seriously. If you're considering employment on the side, your current employer has a right to know about it. It is very likely that the papers you signed way back when you started out say something to this effect.
Even if you are 100% sure that your side-projects have nothing to do with your current employment, and that there is no risk of conflict-of-interest or confidentiality issues, your employer has the right to know, and decide that for themselves. In all likelihood, there's not going to be a problem, and you'll be able to go forward without worrying about keeping secrets. If your employer does have a problem, then you really do need to take their views into consideration before going forward.
To clarify language regarding 'right to know', and 'responsibility': It is my opinion that, in general principle, your employer really does have a right to know about outside work, an exercise judgement over possible conflicts. More specifically, professional engineers will also almost certainly have legal obligations to this effect. (I use 'professional engineer' in a legal sense. In Canada, by law, the title may only be used by member of a professional engineering organization, which is a provincial regulatory body. Things do vary from country to country, but my understanding is that such organizations are the norm in the developed world. If you don't know how things work in your jurisdiction, you're probably not a professional engineer in this sense, so you probably don't have to worry about it.). I can say for a certainty that what the OP proposes to do is explicitly disallowed by the Professional Engineers Ontario Code of Ethics, and is hence professional misconduct for a licensed P.Eng in this province. I'm not going to go through all the different P.Eng organizations' codes, but they are generally very similar throughout much of the developed world. Most of this should get drilled into first year engineering students pretty thoroughly.