I brew a porter from time to time. My latest attempt was "brown bag porter" (recipe:
http://wiki.homebrewersassociation.org/BrownBagBrownPorter) and it came out really nice. silky smooth. Your Munich and golden syrup additions are a bit unusual for the style I think and the lack of brown malt is unusual too. your hops look fine to me.
the biggest thing I've found with porters is to keep the Ph up in the 5.5 range. If you don't get enough carbonate into the mash your Ph is likely to get down too low and the beer ends up tasting thin and a bit sour. I've found that I really have to keep on top of the ph during the sparge too as it tends to dip a bit low towards the end of the sparge and can ruin the first runnings which are spot on. If you typically add acid to your sparge water, you may want to go easy for this style.