finally got some 15lb leadcore. Gonna use it with a millionaire-s 250. Can someone guide me on how to set up the line? Do I use mono backing+leadcore+leader? This is my first time using leadcore and want to do it properly.

Use a good braided line as your backing. You will be able to fit more backing on your reel and the smaller diameter will allow the leadcore to reach greater depths. With the longer leads you will be using with leadcore the braid gives a direct contact to the lure. I prefer using 20lb PowerPro as backing. Also, 18lb leadcore is usually a better choice because it has more lead in the middle of the line and it's the same diameter as 15lb.

what would be a better reel for leadcore a calcutta 700 or a tekota 600? would they be overkill for trolling leadcore for trout/bass/striper?

I've never fished either of those reels but I know that they are big. Personally I use a Penn reel and then a 6500 and 5600 that have smaller sections of leadcore on them. I'm not a big fan of leadcore and prefer running downriggers. How much backing and leadcore you need is really determined by what you're fishing for and how deep. If you're after planters then you don't need much backing because they don't take much line. Using braid will get you deeper than just straight leadcore. Downriggers are really the only way to go if want to deeper waters with precision.

You would be better off using a Penn 109. This reel is a good compromise between reel size and amount of leadcore that you can get on the reel. You can get 6 to 7 colors on the 109, yet the reel isn't much bigger then a standard baitcaster. If you want to run a full 10 colors go to a fly reel (with a multiplier). Its direct drive (you back reel when you hook up with something big) but its far better then using a 10 ton ocean reel. Shoot me an email if you want more info. I also prefer to use downriggers, but at times leadcore does better... :-)

-scot