I'm no expert in HE's but i think i know the way they work.
By using lothern sea gaurd you have to play defensive to take advantage of those lovely bows.Try and get RBT's as they will help with the shooting phase. High Elf mages are awesome due their ability to pick any lore in the rule book and their own and still get +1 to dispel just because your a HE which combined with the way levels work mean a high elf gets a static +3 to dispel attempts if you bring a normal lvl2 mage.
Anyway always bring mages , for lores pick one with life and the other is up to you.
Dragons took a large hit due to the points limit for lords. If you are interested in bringing a dragon make sure its the prince with a great weapon and spend the rest on defensive gear. I don't know the names of the armour but uou can easily give your prince a 2+/4++ with armour save rerolls.
Persoanly though i think i lvl4 mage might be better than a dragon in the current edition for your lord options. Also believe when i say the dragon model is a pain to transport. My bro collects them the wings are prone to braking , if you buy a dragon don't glue the wings on , they have lugs so they can slide in the hole anyway.
I would bring in low point games 2 lvl2 mages and a BSB and higher points a lvl4 mage a lvl2 and a BSB. High elves already have a good leadership so a good general isn't mandatory but a BSB always helps.
If you can buy more lothern sea gaurd that would be great , there are lots of bits websites that stock cheap parts like the new lothern sea gaurd.I'm not sure how many to get but 2 units of 25-30 is pretty solid.
BTW what does the battleforce contain?