It depends on the area you want to stay and what you are looking for in Manila. Lots stay in Makati area of Manila. Especially near Greenbelt if it is near the Malls you want to stay. Greenbelt also has a lot of restaurants of great variety.
As the other OP said Grab out of the airport is the best option for a first time visitor.
There is a Grab booth outside arrivals. DO NOT let people try to get you a taxi other than the official one Grab. They would be wearing Green uniforms. They would ask for your details and then book you one to your destination.
Exchange your currency at the various banks immediately after you exit the customs area. Then buy a SIM card. I would recommend GLOBE as their coverage is better. It is the rainy season so an umbrella would be helpful.
Hotels are not cheap but again it would depend on the area where you want to stay. Public transport is terrible so look to have grab or Taxi. It would be better if you can download the Grab App but bear in mind when it is raining it is very tough to get a grab or a taxi.