@nicolaclyon 

QBSE only offers limited features for your case. Your best option is open a Wise business account to accept payments in GBP, USD, and AUD from your clients, convert the balances to GBP account anytime you want, and run the bank feeds into your QBSE account. You may withdraw your balances easily anytime with a competitive currency rate and a lower fee to your local bank.

https://wise.prf.hn/l/64dl92k

Second option, use QB Desktop US version with a one time license. Then utilize a time tracker app to integrate with it.

http://hubstaff.com?oid=1&affid=94

Last option, switch to QBO Global version for Spain.

https://quickbooks.grsm.io/EU

then explore these project management apps to integrate with your QBO. .

https://teamwork.grsm.io/quickbooks

https://paymo.grsm.io/quickbooks