Unlike in American English, in British English 'shall?' is often used in questions when we are making offers and suggestions. However, "When should we start?" is probably more common than "When shall we start?, even in the UK. If you want an alternative to 'shall' in questions, just use 'should'. It has the same meaning and is equally polite.

To my (American) ears, "shall" doesn't come up much in conversation at all. Usually it's used if someone wants to be deliberately old-fashioned or very very formal, usually in a joking way. Common alternatives: "When SHOULD we start?" – implies there's a specific timeframe you want to know about "When DO we start?" – probably the most standard and polite "When CAN we start?" – more informal, might imply impatience, i.e. you really want to get started soon! "When MAY we start?" – probably the most polite of all, but it's also not very common to hear outside of very formal situations (like job interviews or business meetings) This might be different in British English, however. I think "shall" may be in more common usage there, but I'd have a person from the UK confirm that. :) Hope this helps!