We use quickbooks online to track our time, payroll, and income and expense tracking. 

@Greg Strunak have you tried the anti-barking devices they sell online?

I've reached out to a couple I've found online but they were unprofessional and didn't inspire much confidence--and then they didn't have any deals.

Recently I heard an online property insurance company advertising on one of the BP podcasts, but I can't remember what the name of the company is.

Ally and Discover have pretty good online savings accounts.

Are there other ways to invest idle LLC cash in online savings or money market funds? 

One of your biggest challenges will be separating all the online fluff from reality.EXAMPLE: several S8 "gurus" have already been exposed as frauds, but unfortunately, they sucked in thousands of investors.You're an engineer, use your education & experience to start building up a logical approach to investing in rentals:)Start with this:Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.So, when investing in areas they don’t really know, investors should research the different property Class submarkets.

Looking for a good online program for tenants to pay rent.

When I look at other short term rentals online, they're all shacks for $80-100+ a day.

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.