Just received my first companion voucher but have no status yet with BA.

If I book MAN-LHR-LAX-MIA-LHR-MAN in Club World for myself and my wife using this companion voucher, can I use the lounges at Heathrow, Miami and Manchester? (What booking class should it be as the MAN flights will book into Economy)

Also, when using this voucher online, is it correct that I pay just the taxes for both my wife and I and also redeem 100,000 miles for the above trip?

Any information\tips would be helpful when using companion tickets.