Well, first of all, it's hard to beat a good lever action. They're handy as a pocket on a shirt, they're usually very reliable, they're very fast-handling, often capable of darned good accuracy, they're usually reasonably priced, and, most importantly, they're well-received by the public and don't cause alarm.
To answer your questions, by the numbers:
1. Marlin vs. Winchester?? (I like the feel of Marlin I as of todays trip to the gunshop)
Coke or Pepsi? Mercedes or BMW? Mustard or ketchup? Go with the one that feels better to you. Sounds like you favored the Marlins. Strictly comparing Marlin 336's to Winchester M-94's, I can tell you that, on the average, the 336's shoot tighter groups than the M-94's, but that the M-94 actions are usually slicker, and feed better. Regular '94's had to have an offset scope to the left, as they ejected straight up. I don't know if all '94's are now "Angle Eject"; some are, at least. 336's are all "Angle Eject", and you can mount a scope right over the receiver, thereby making your handy, sturdy little carbine into an ungainly, delicate rifle. But to each his own. Each is tapped for receiver peep sights. (HIGHLY reccomended.)
2. What caliber is best in a lever action?? (30-30 looks good, but .357 is interesting because it matches many of my revolvers)
I like .30-30 over .357. .30-30 is no great power-house as a rifle cartridge, but it
is a rifle cartridge. It's thick on the ground, and very cheap, as loaded ammo goes; well-under $10/box, usually. This business of mating your pistol ammo to your rifle is an excellent solution to a problem I've never yet encountered, nor have I met anyone else who has. It is a very rare thing that you would EVER need more than 10 rounds of rifle ammo for a hunt. 5 rounds in the magazine and 9 on the buttcuff on the stock gives a man 14 rounds of centerfire rifle ammo, and that's generally enough to fight the good fight! .357, however, is really a bit sparse at 100 yards, even through the carbine (it only picks up about 150 fps in velocity. Some loads maybe 200 fps...). I personally do not think of the .357 carbine as a 100 yard deer combination, nor do I feel it's really adequate as a defensive rifle. It only slightly extends the range beyond your pistol.
Other options would be .45-70 (oh yes!), .35 Remington (basicaly just like the .30-30, but the ammo's not as common, and it costs more, usually), .44 Magnum (better than .357, but not as good as .30-30. Oh yeah, you didn't say you had a .44 pistol. Maybe an excuse to get one...
), .444 Marlin (almost as good as .45-70... nah!), .45 Colt (fun! But see .44 Mag.).
Or, you could get a Browning Lever Action (BLR) in .308 (lightweight version), which can shoot spitzer bullets (with better ballistic coefficients) because of it's detatchable box magazine. These are more expensive, and aren't cowboy at all, and are very cool, nonetheless.
3. Does Marlin make more than one model of 30-30 and what barrel length is the handiest?
They do, and I like the 336 the best. 16" is really, really handy, but for sight radius and reduction of blast and better velocity, go with the 20".
4. How much should I expect to pay for a new rifle? And is walmart a good place to buy?
The mid to high $300's. Wal Mart is
not a good place to buy. The service just isn't there, and you're screwing your local small gun shop when you go to the MEGA store that sells with a 4% profit margin. Buying from Wally World saves you a couple of bucks now, but puts your local small shops out of business, leaving you only Wal Mart. This leaves it up to THEM to make up THEIR minds as to whether or not to
let you order pistols through them (they stock NO pistols, now, so you can't handle them in advance), and to decide if they will keep selling them low, or to jack up the prices, as they've done in the past with drug stores and other shops.
I love free enterprise, but believe me, you're getting much, much more for your money if you'll just spend it at your favorite local gun shop. Don't have one yet? Ask around. You MIGHT find a good deal on a nice used one. These things are very often traded in at pawn shops, with plenty to choose from.
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Wow. How I ramble. Hope this helps.
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Will you, too, be one who stands in the gap?
The lever-action is alive and well as a modern incarnation, and you should not be ashamed of utilizing new materials for stocking and finishing it any more than you would be ashamed of using modern powders, modern bullets, modern steel (metalurgy has come a fair piece in the last 100+ years!) to get the most out of your rifle.