Video Card selection and questions

[Topgunben]

Hey folks,

Just building a new computer. Going with the following:

Ryzen 5 3600 CPU
2x8gb 3200 ram
SSD for storage


My question:

How much worse would it be if i bought an additional R9 280x and crossfired, versus going with a RX 5500xt?

Its about a $100 less if I crossfire with my old GPU. Its only $100 but if the performance isnt that much of a difference, id rather crossfire now and put the money into a GPU down the road, when the $450 GPU that i want drops in price.

Additionally, What are your thoughts on running dual GPU's in general vs one single? Are games utilizing dual GPU's as much as a single?

Thanks