My usual advice is to buy a used, high quality rifle, from Tradex for about the same price you'd pay for the new commercial pieces priced to attract those on low or fixed incomes. When I was a youngster the logic was to buy a Lee Enfield for $30 or less, and even then, many of them were junk, and I don't wish to inflict that learning curve on anyone. However, lately I have come to modify my opinion, if only slightly, to the extent that there are some budget rifles that have features combined with attractive pricing that makes them worthy of consideration. After visiting WhyNot this past summer, He pointed out some features of the Marlin bolt gun that impressed him, and if its good enough for Ted, who am I to argue. As to the choice of stainless or carbon steel, I doubt it matters. Either will give years of trouble free service if looked after, and both will let you down if ignored and abused.
As to the chambering, I don't think it matters very much either, except to say that a light rifle will be more challenging to control than a heavier one as you climb the power ladder. If for general use, which for most folks means to include moose and bear, I would be content with any cartridge between the 6.5X55 and the .30/06. Of the three cartridges you mentioned, I would rate the .270 as the best, with the 7-08 snapping at its heals. A pal of mine is a real fan of the .25/06 , particularly when loaded with TSXs or Accubonds, but to me the quarter bores don't come with enough bullet weight to recommend them as suitable for general purpose cartridges. FWIW, he now shoots a .280 Remington, and this is another excellent choice that is far too frequently overlooked.