I think you should fix the leaking pipe first. maybe invest in the $7 springs?
you sure do want to buy a lot of things for it now. Reeds, a jug, now a tach.
i would rather have it running perfect and reliably before i start adding extra parts that are not needed.
so, onto the tach.
there are digital tachs and hour meters that work okay. but nothing great.
there are universal tachs made for offroad vehicles, but there is no way to know what the settings are.
being as there are 3 firing types between different engine, it would be hard to find one unless you have one you can change the setting
might i suggest a trailtech kit. i used the vapor with good results.
engine temp, rpm, speed, hour meter, odometer etc. worked great and it only ran off a small battery
if you connect to power (with the dc converter you linked) the back can light up for night riding. and you can set shift lights to come on at certain rpm
there is a primary and secondary shift light. yellow being "you can shift now" and red being "you need to shift now" and you set the rpm as desired