1. To be chartered you need to attain a Master's degree or demonstrate Master's level of knowledge. You can go the degree route two ways: get an MEng degree or get a MSc degree after a BEng degree, any degree you get must be accredited by your chartering institution of choice. Once you get the relevant set of degrees, you can usually apply for Chartered status after 4 years of work experience in an accredited workspace.
2. Getting a MSc after a MEng is redundant as they both share a lot of modules, furthermore many good universities do not accept you for a Master's program if you already have Master's degree. In terms of value if you were obtain MEng it would be academically equal to a BEng + MSc combo, they have the same value, however some employers may prefer MSc if you are going into specialized work as the MSc is more about specialization, along with the fact that it is a postgraduate degree (it requires more time in university than a MEng degree).
3. As far as I know taking a year abroad does not affect the value of your degree, it still holds the same academic value, it is just up to employer preference.
4. BEng is usually offered in engineering field only such as civil, electrical, mechanical etc. while BSc is usually in physics, chemistry etc.
I tried my best giving the knowledge I have as I am only in my first year of BEng degree, hope it helps.