does it have wifi? If not, how can I add it?

No, it does not come with pre-existing wifi, but you can add a pic card or a USB wifi dongle.

Does it have a PCIE 16 slot available?

Hello, Thank you for contacting us in regards to your question. Yes, for a low profile type GPU. Thank you, Newegg Support

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Dell Desktop Computer Optiplex 7020 Small Form Factor SFF Intel Core i5-4590 3.3 GHz 8GB DDR3 128GB SSD DVDRW Windows 10 Pro 64 Bit

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