If you decide you want USB.3.0, a USB 3.0 PCIe card can be added.  The only caveat being a USB 3.0 extension cable would have to be ran from the back of the unit.

Congrats on your Optiplex purchase! I've been a fan of them since probably the early 2000s.I bought all of mine secondhand.  My first one was an Optiplex 200 from 1997, and worked great until I got rid of it in 2009-ish, and even then it was still working; it was just too slow to run anything. My next one was a GX270 (2007) which served as my audio editor PC, and ran until the motherboard finally died in 2021. I currently have a 7020 SFF and a 9020 USFF.  (I may try and go for a 9020 MT next.)

A quick note on your PC Specs and upgrading: Your RAM is maxed out at 8GB; it won't see any higher. However, you can upgrade the processor. It can take an i7-2600 as the max processor, so you'll get a little bit better performance. The 390 originally came out in 2011, so it's pushing 11 years old. You should be able to get at least another 2 years out of it, based on personal experience.

Thanks! Also do you know why when i boot it it gets seriously loud then suddenly stops to normal volume?

Okay, will do that in the future!

Nope.  By any chance did you buy it refurb?  Is the inside and everything clean?

In case ever needed:

How to Troubleshoot Fan Issues 

Re: do you know why when i boot it it gets seriously loud then suddenly stops to normal volume

that is the normal behavior of Dell bios for older model.  Before it completes POST the bios drives cpu fan to full blast and then turns it down to normal as soon as POST is complete. which usually takes 1 second.  Dell uses server grade oem fan which can be quite loud like a jet engine sometimes when revved up.  in older XPS desktop this gives a pc a race car engine roaring sound which might be intentional.

In some Dell PC if POST has stalled, the loud cpu fan would persist which is a sign of failed firmware test.  

That's a good answer.  Yet, my dad's 390 doesn't have any jet engines so it won't be flying away anytime soon.

OptiFlex airlines? Jokes aside - thanks for replying.

Thank you, thats really helpful.

I bought it refurb for £50 on ebay, thanks!

Good one.