also should I wait to put in a new central air unit until the new year or put it in before the new year.

Yeah, it costs a bunch of money to put in.  

I'd love to put in a steel door, but it's almost prohibitively expensive.  

This would be my first deal as a real estate investor and as we purchase our first property, we are contemplating about the structure to put in place.

If you only have 1 or 3 tenants, you may get away without formally tracking each one in a ledger / customer account but once you grow beyond that, a system needs to be put in place.

Would much rather have an area rug and a wood floor than a carpeted floor, and I've removed all carpet from every property I've ever owned...buuuttt if I were trying to rent to Jim, or in an area that had lots of people like him, I'd put in carpet in the bedrooms anyway, since it's more likely to rent with the proper floor coverings for the area.

No tenants present means less distractions and getting the job done sooner. 

I was able to get a higher quality tenant, that stayed longer put in roots and our average time a tenant stays is now 3 years.

If I am going to be spending money on a sprinkler system, I might as well put in a drip system only and do just the xeriscape idea.

If you start to do several projects a year and use the same contractors regularly, you can build a relationship where you can call them to meet you at a property ASAP so you can put in an offer knowing what the cost will be.