I think you need no more than 5 GB of space, if you have a Discord account you can find the bootstrap in the dedicated channel of the Gobyte server.
I did not check total space after I synced my wallet but the synchronisation is very quickly.
I used STEX in the past and did not used it for many months. Yesterday, I tried to do KYC with them and their KYC requirements are complex, with requirements for personal bills, etc. I gave up with the step and in my opinion, HitBTC is the best exchange to trade Gobyte.
The altcoin season is existing and I hope the team will do some initiatives to bring Gobyte to other exchanges that don't have mandatory KYC like STEX.