Drain line - is it a blockage or back slope / kink?

I just installed a new toilet in my basement bathroom. The previous owners had a toilet, but it was old and everything a too low to the ground. Anyways, the house is 1971 and has a "old" oval type shut off valve that had been closed for quite a while since the old toilet wouldn't stop running and we never used it, etc. Got my new toilet hooked up and everything works great and I don't see any leaks, except the oval shutoff valve LEAKS pretty quick when I open it fully. This is the one of course that connects to the toilet to fill the tank. I've got it really close to the closed position and so far there aren't any leaks and the toilet fills fairly quickly still after flushing, etc. Is this ok or should it be in the fully OPEN position? Right now it seems to have stopped leaking, like I said, but I don't know if it's IDEAL to be mostly in the closed position. Thanks

Not really sure where to post this so if a better place please kindly modarator move it for me. Very long winded but need advice and opinions, We moved into a fixer upper about 2.5 years ago, A 4 story if you count the basement home built around 1909, Sometime in the last 20-30 years most of the supply water lines were replaced with copper, one upstairs bathroom didnt get ran, it looks like an untouched 60s 70s unit, The other upstairs bathroom had the copper supply ran and capped off, The antique high tank toilet had been seated to floor, tank mounted on wall, No sink, A huge 6 ft claw foot tub on blocks rests with the drain over a big hole where they removed a galvanized tub drain pipe replaced with pvc, the ceiling under this area shows a sub par repair from water leakage, in my guess from a plugged up galvanized pipe. I got all the parts hooked up the toilet, it works great, i was really excited, im over 50 but never that i recall flushed a high tank before, But my crest quickly fell, As then i learned the vertical galvanized sink drain was packed full of a rust, bummer i started cutting sections out but in doing so and testing it and the the bathtub drain the galvanized pipe they have the sink and tub pvc drains plumbed into is shot, too full of rust needs to be replaced with pvc, So here are my hurdles and questions and need for other minds on this, Basically the only way to get this junk galvanized drain out or disconnected from the main drain where is connects is to cut through the floor some more, but the floor is weird to me, It starts as tiles then about 4" cement, then what appear to be 1" x 5" planks some different weights then a drop of about 6 to 8" and the top of the ceiling of the rooms the bathroom is over, I realize replacing the plugged up galvanized pipe is a must, my wife suggested a small snake in a drill but i dont think it will help or be long lived, the sink drain i did cut out even after i cleaned it appears about 1/2 restricted with rust scale mess, If i make another big hole to get at the pipe how do i mend that hole and the one for the tub drain, I dont want to jack hammer all that creat out, in fact im going for a very rustic imperfect look in this bathroom so the floor need not look perfect, Do i have to replace the planks and pour 4" of cement in these repair areas, any way to build it up but not use 4" cement? How do i support the planks where they have been cut out? As luck has it there is a stock of this same tile in the basement that has lots of old plumbing and electrical stuff stockpiled, Im a bit depressed on this set back as the floor and its repair are at the moment a mystery to me, Many thanks, B