Ok, you don't need FRB to lend money, but it surely increases the amount that you can lend and therefore decreases the cost of lending.  Otherwise lending will get much more expensive.  Will it not?>

Nope, there is no problem in lending bitcoins. The FRB doesn't make lending possible, FRB only by fraud allows banks to do the lending instead of the rightful  owners. Despite the fact, that it decreases the lending costs, but it also increases overall prices, so in sum there is no benefit. Actually there is a net loss of what bank earns on it while not being a rightul owner of the funds.

So with 100% the lending is possible, yes the lending costs will be higher, but at the same time the amount needed to lend will be much lower, since there won't be any induced inflation caused by FRB.
In sum, the 100% reserve banking is much more beneficial for the individuals (both borrowers and lenders), the FRB is beneficial for banks only (they earn interest on things they don't own damaging all other participants on the way).