Consider the Nikon D7200. That is what I upgraded to from a D3300. It lacks some things...like an articulating screen...but has other things....dual card slots, and a focus motor which lets you use less expensive older lenses. You can get one for around $700.00 used, or $900.00 new. It is a Nikon DX model, so it will use the lenses you already have. It has a bigger buffer, so you can shoot more action shots before slowing down. It can shoot time lapse movies. It has 51 AF points. The built in flash can act as commander to control off camera flash units. The top shutter speed is 1/8000 of a second. It is sturdy, being mostly made of a Magnesium alloy. A battery grip is available. If the articulating screen is important to you, consider the Nikon 1 J5. It is a small-point & shoot sized item which takes removable Nikon 1 mount lenses. It is mirrorless, costs $500.00 new, or about $280 used, has a lot of handy features, and-with a Nikon FT-1 adapter-can use Nikon F mount lenses (DX,and FX), like the 50mm F/1.8 you already own.The Crop Factor on the J5 is 2.7...so your 50mm lens will provide the field of view of a 135mm lens.