i did this on my starlet 3 years ago, you will notice straight away an acceleration boost and that it warms up quicker, i suggest a hotter thermaostat while your at it, believe me it makes a difference in warm up times, as for wear on water pump, mines 3 years on and shows no signs of giving up so dont know where you heard that from.
when i did my conversion i gained 1.6kw on the dyno (thats a 3-5% gain for me
believe me it is worth it and it takes a load off the motor bearings as it has less mass to try and spin
if you want anymore answers feel free to ask no matter how stupid they sound