The stock static compression ratio is 10.0:1, which is a pretty good figure in my opinion, if modifying I would aim to keep it around this. It's not low by any means, and it's also not so high that it'll be hard to tune to run correctly on pump fuel. 95 octane premium unleaded will need to be used, but you shouldn't need 98 unless you go crazy with mods.
Calculating the compression ratio of a modified engine is a bit involved, it requires lots of accurate measurements and some maths to work it out. There is some good info here:
https://www.rbracing-rsr.com/compstaticcalc.html
When I was doing some of these measurements on an engine I'm building I bought some specialised tools, including a deck bridge, which allows a dial indicator to be used to measure piston height relative to the block deck.
Something to keep in mind is a factor called "squish clearance", which is the distance between the top of the piston and the flat surface areas of the head, measured in thou. If you get the clearance as small as is safely possible, you help to concentrate the combustion in the centre of the cylinder, and reduce the tendancy to ping/knock, which means more power on lower octane fuel, and easier tuning. You can alter this clearance by machining metal off the block deck, or by using a thinner head gasket.
Engine work, be it rebuilding or getting it modified, is very expensive work, largely because it's quite time consuming, and the equipment used by engine workshops is bloody expensive so they need to make a return on their investments. They will typically have ten or more different machines for milling, grinding, boring etc. and many machines cost over $10k.
