Fortunately, cost segregation is a valuable strategy that real estate investors can use to optimize their tax savings and enhance investment returns.

Your taxable profit is based on your cost basis, perhaps enhanced by margin...Similar for real estate. 

I do plan to hold for long term.I am getting mix advice: some said keep things the way they are, sand, and paint the trim, fix sash lock, install insulation strips, while replacing a few exterior sills, and not worry about tenant wanting to open the windows..Then I am told, go ahead and do it as a good feature to attract tenants (new, save energy with ensured/enhanced insulation, utility will be paid by tenant), of course the windows can be opened like they suppose to, less maintenance headache with possible landlord call for window breakdown/issues.

It sounds like you have some minor improvements that could be made (fencing), that would enhance the attraction of the home to a buyer. 

I will not need any income from the portfolio while it is growing.I wish to pick a strategy that uses leverage to (sanely) enhance growth.

I love the minimalist approach to staging...gets the job done enhancing the space without breaking the bank.

Additionally, I use a software for tracking and managing my cleaners’ tasks, allowing me to monitor their progress and address any issues promptly.To further enhance the quality control process, I’ve instructed my cleaners to upload images while on-site, allowing me to visually see their work and identify any areas that require attention.Consistent cleanliness has not only translated into positive reviews but also increased booking rates, making my earnings higher!

All are paid for, all are solid properties, all are rented with students, no repairs needed, simply undertake enhancements projects.What are some ways to finance my next purchase? 

The interest yield on the transaction also can be enhanced.

Also look at ways to enhance your plan in those 12-18mths... such as consolidating your loans etc.