i would get an engine flush first then go for some castrol magnex its expensive but will quiten down the noise a bit should clean out the old engine oil
i would use any oil fillter wont make a diffrence
if your going to fit lowewring springs fit shocks as well because asfter time the standard shocks will break and lose the hydrolic oill in then which will fail an mot so my advise is to lower the car and fit lowering shocks as well as springs