VQ35DE was in 2003-2006 then after that it became a VQ35HR for 2007+ models
Early DE engines had 276bhp and 6600rpm rev limit. Yours has 300bhp and 7000rpm rev limit and the HR has 313bhp and 7500rpm rev limit.
UPREV is tuning software. A good tuning pack is a full exhaust system, panel filter, plenum spacer then UPREV Tune.
Welcome
PS: decent tyres are equally important.