Your point (2) first. Manually focusing a Contax G involves rotating a somewhat fiddly wheel until you get the distance setting you want. On my G1 (I believe the G2 is the same),this wheel has the annoying habit of rotating itself while I'm out shooting, and more or less auto-resetting the distance, usually to one I didn't want to shoot. As the viewfinder doesn't focus inor out according to distance set, often as not I don't realise this until I've shot an entire roll. Frustrating, to say the least.
I get around this annoying G 'trait' by sticking down the wheel with adhesive tape. Which is still an annoyance in a camera that as I recall sold for almost A$2,000 (body only) in Australiain the '90s and early '00s.
So yes, manual distance setting is possible. The G1 instruction booklet has a focusing distance chart, so you can calculate what will be sharp from foreground to background,depending on what f/stop you use, if you can be bothered to take the booklet with you when you shoot and refer to it as you go. Or make a photocopy of the page and laminate it, as I did, 'tho after 15 years of shooting with my G1 all the f/stop-distances areburned into my brain cells..
Your Point (1) now. I'm sorry that I cannot be of any help to you in this,as I've always shot my G1 on aperture mode and even then usually at f/5.6 or f/8. I am in this sense, a very predictable photographer, technically. There may be a way to manually set the two separately. Someone else on this site will assist with this information, I'm sure.
To me, the strongest point in the Contax G range are the superb Zeiss lenses. The G lenses were manufactured in Japan by, I believe, Cosina, but they are astoundingly sharp and produce lovely crisp colors and mid tones.
IF you are determined to do it all manually, you should perhaps explore other options in rangefinder 35mm cameras,such as the Bessas with the wonderful Voigtlander lenses,or possibly bite the (financial) bullet and invest in an M series Leica and a few carefully chosen Leitz (or again Voigtlander) lenses to suit your shooting style.
Whatever you decide, there is rather a learning curve with the Contax Gs. Fortunately, I took to the camera like a duck to water, and it produced some superb color slides in the days when I shot Ektachrome and Fujichrome. I now and then have to scan some and I always marvel at the amazing colors and mid tones. Also black and white negatives.
Of course the Voigtlander lenses are capable of producing the same wondrous results.
Whatever your ultimate decision, the rangefinders are wonderful cameras and well worth using.