Business startup in Porto for expat moving to Portugal soon

Hello

Was wondering if there were any useful 'howto's for people wanting to startup small businesses in Portugal?
In particular, interested in the issues of transitioning, for example the catch 22 of having to register, and get a business bank account and not be able to trade while this is being processed?

I know in the UK the tax authorities are pretty lenient on sole traders so long as you are up front with them, and it seems much simpler and cheaper to get setup.

Any advice appreciated... for example, as EU residents can wait 3 months to get registered as permanent residents, can they trade with a UK address/company in the meantime? This may work as we are not entirely sure if we are going to stick it out.

All options/any tips that people have experienced greatly welcomed.