[susan53]

1. Yes and yes
2. The problem with the examples sentences that you've used is that they're so unnatural that they sound strange anyway. But However would normally be restricted to neutral and formal contexts, whether spoken or written. Here are some examples from spoken English, both in a neutral style :
a) But the theory is that if we, if we get to know what the, the purpose er of the job or, or the assignment is, er then we, we stand a slightly better chance of er getting a satisfied client at the end of the day. However, it's still a vague definition and we often find it more useful to er tidy that definition up by introducing, conformance with requirements.
b) ...because it was probably the first time they had formally quoted a price. Er, however erm because of the concern about er the overall cost of the programme and the production cost in nineteen ninety two