Expressflight
From your description I assume the ILS and associated lighting will permit operations to landing minima of DH 200ft and RVR 550m. I agree that 200ft is unlikely to be an issue, but 550m RVR certainly will cause problems from time to time. SEN's fog record may be good, but it's not that good. It may not suffer from LTN's topographical issues, but it experiences radiation fogs like most other UK airports and also coastal advection fogs.
A pity therefore that the "new" airport will not support Cat2/3 operations. Presumably this was investigated and rejected - on the grounds of cost, or site limitations and practicability ? Of course it can be argued that LCY and SOU have managed very well on Cat 1 only.
Crosswinds should not be an issue. In my experience the 757 was restricted only on a 30m wide runway, not 37m as at SEN. The A320 had no such restriction and I would expect the A319 to be similar.