Engagement party deco ideas?

Ok so I posted earlier that I am having a last minute engagement party. 160 people invited

Anyway it is a backyard party. We are setting up tents and have tables,chairs and linens rented.
We have 4 servers, a bbq chef, clam bar and two bars...so I figure I can class it up a bit.

OK so for the tables...would you let people sit where they want since its a backyard?
Can I still make table numbers or decorated frames without numbers naming the tables?

ALSO
on the tables bowl with a floating rose...do i do small candles with them and how many? The tables seat 12.

Any other decorating suggestions?

Thanks ladies!