that one is a 4.1 not a 5.1 (see the date says 2009) it's a 4.1 with the firmware upgrade which is fine but means it's a tad older, the GPU will need replacing and you may want to buy a SSD for the os and at least 1HD for your video files.
if you look here you can see the cpu upgrades you can do
https://forums.macrumors.com/threads/mac-pro-cpu-compatibility-list.1954766/
i got a W3680 from ebay and installed it myself (got it for £80 about 90 euros) but the W3670 3.2ghz 6c is a lot cheaper and not much slower. (there upgrade price is ok i gess)
you will want more than 8gb of ram but unless your doing complex stuff 16GB is ok (i got 32GB for £50 about 60 euros but i tend to at most use 20GB relay)
id buy ram from ebay there upgrade price on ram is to high but thats up to you.
for GPU you will need something faster but you dont need to go crazy as relay in thouse apps it's not used in a huge way you can get a GTX670 fairly cheep (you will need to buy two 6pin to 6 pin power cables for it but a pc card is fine)
i use a pc GTX660 which works fine for me, id advise you not to buy a expensive one at the mo as soon it looks like the RX 470/480 will work in osx which will be far better than any outhere card we can use at the mo at that price.
you can see my macpro 5.1 upgrades in this topic
https://forums.macrumors.com/threads/just-got-a-5-1-looking-for-ram-cpu-tips.1968018/ some things are a tad old but things like links to ram still seem to work ok