@Henri Chow, my partners and I run a very technology-focused (and tech-curious) QI and we tend to get a lot of clients that like good, simple, sleek, automated services. 

Do you use old-fashioned excel sheets for keeping track of expenses and revenues or do you recommend any other software or technology for this task?

I'm very well Versed with Technology & Social Media.

Here are some examples of the recovery periods from the IRS 996 Publication:5-year Property: Automobiles, qualified technological equipment, office equipment (copiers, calculators, etc.), appliances, carpet, and furniture used for residential real estate.7-year Property: Office furniture and fixtures (desks, filing cabinets, safes)15-year Property: Certain improvements made directly to land or added to it (such as shrubbery, fences, roads, sidewalks, and bridges)There are multiple approaches to cost segregation studies including the Detailed Cost Approach, Detailed Cost Estimate Approach, Survey Approach, Residual Estimation Approach and Sampling Approach.If you feel like you or your business could benefit from a cost segregation study, first speak with your accountant to see if the tax savings outweigh the potential costs.

I personally think they are super easy to invest in remotely with a good cleaner / repair person, and a little bit of technology but I did do a couple of long term rentals locally. 

Residents of this segment are physically active and up on the latest technology.

What is your go to resource / technology for looking up phone numbers for landowners?

Depending on the real estate you own, you may want to also look into 5G leases for WiFi, cell towers, radio and other technology applications on your property's rooftop.

It is a long term hold move and then its an issue of by the time it pays the technology may need to be updated.

I come from the parking technology field and have held RE licenses in HI, FL and now TN.