Fully battened main
I have a lot of time sailing boats with fully battened mainsails, normal battened mainsails, no battens, and mainsails with one or two full length battens. I strongly prefer mainsails with one or two full length battens at the head of the sail and a couple slightly longer than normal lower battens. Having full length upper battens has all of the advanatges of full length battens, namely; allowing additional roach, reducing flogging in heavy air and better sail shape for beating.
Only having only upper full length batten(s) eliminates or reduces the problems normally associated with full length battens. The mixture of long and short battens means that you have less friction raising and lowering the sail than you would with full length battens. You don''t have the problems of chafe and broken battens when reaching and jibing. It is easier to see what is going on with the sail so that you can trim the sail more precisely. In light air it is easier to get a properly powered up sail.
A couple other suggestions, having the battens parellel to the boom makes reefing, and flaking easier and reduces slug friction at the mast. Consider using higher quality and longer sail slides at the full length batten position. Consider a loose footed mainsail. Make sure that your reef tack and reef clew cringles are properly reinforced and has high quality leech line cleats at both reefs that are automatically released when tensioned from the cleat(s) below. Make sure that the sail has chafe patches at the spreaders. Make sure that the slugs either side of the reef points are spaced to permit you to tie in a reef without opening the sail tracks.
Enjoy your new sail.