Let's start by examining your barrister's optimism:
The sentencing range for GBH is 3 to 16 years' custody but those sentences can be cut by up to one third for an early guilty plea. So that means that the effective sentencing range (where a defendant pleads guilty) is actually from 2 years up to 10 years 8 months imprisonment.
The maximum sentence which can be suspended is one of two years' custody. So your barrister is hoping that the court will pass the ABSOLUTE MINIMUM sentence AND that the court will then see fit to suspend it. If the court decides that just a very slightly longer sentence (of, say, 25 months in prison) is appropriate, such a sentence CAN'T be suspended.
So there's a great deal of optimism required if you're hoping for a suspended sentence; it would still be best to pack a bag when you go to court.
However if you do receive a suspended sentence, and it's the ONLY sentence that you receive, then there will be nothing to prevent you working in Greece other than, possibly, the prospect of you being refused a work visa by the Greek authorities. (As the UK is no longer in the EU, you have no automatic right to work in Greece. You'll need to go through the visa application process).
However suspended sentences are often accompanied by supervision requirements, requiring offenders to attend regular appointments with the probation service. If such a supervision requirement (and/or a requirement to undertake unpaid work) is imposed, you won't be allowed to leave the UK for a 4-month period.