I have done this several times to my family's advantage in order to supplement our retirement income but instead supplemented our current income.

Not sure how this works in your state but you could have a supplement if the sewer goes above a certain average rate you charge the overage.

I would like to end up with 4-10 doors to supplement my income.Do you have any relatives or friends that have RE experience?  

But if you choose your major wisely, and supplement it with good electives that can enrich your education, then college can not only make you successful financially but also make you a more well-rounded educated person.    

Yep HP (really just exchangers) will need electrical heater strips for supplemental) Enthalpy calculations tell that story but resi HVAC guys rarely know this.

Most of their training is using trusts for estate planning.I belong to an informal CA trust study group/mastermind & I supplement that with what I learn from others such as Ward Hanigan who lives & invests in CA.Be very careful trying to apply other states practices in different states.

Supplemental income from RE can help make any of that happen.

At first I would like to simply supplement my income, but within the next 5 years, I would like to have entirely replaced that income with investments (multiplex, STR, ect). 

We BRRRR 1/3 of projects and flip the other 2/3 to supplement and money left in the BRRRRs.

We BRRRR 8-10 per year and the flips supplement and money left in the BRRRRs.