Gauge Question.....

[gor131-x]

i was looking at this site for some gauges in my car,im going to change it to a double din(eventually!)
this is the site:
http://www.42draftdesigns.com/specials.htm

anyway,i was wondering, you know the boost gauge,well,one gauge i saw reads up to 15psi and another reads up to 30psi,which one would i need ? i have a 90bhp tdi remapped to about 120bhp

how much boost do our cars give off according to these gauges?

another thing,i know for the battery you need the voltmeter,what do you need to check the oil level,is it oil pressure or oil temp?(stupid question i know)

oh and does anyone know any cheap gauge places other than this

any advice or help would be appreciated

Thanks