OP, ignore the "woobie warfare" if you can
best advice on caliber was already stated... depends on what you do
likewise best advice on type of sights ... depends on what you do
45-70 or 444 w/ high X power in heavy brush, 300# angry hawg, scope nope
BLR in 308 for antelope 200-300 yards, high X scope, good choice
nice thing about lever guns like the Marlin, you can easily try all flavors of sights with minimal pain
PS
peeps work great for some old eyes, but not mine old eyes
I vary between open iron, red dots, LOW X power intermediate eye relief compact "shotgun" scopes 2.5X or less (and the both eyes open fast target aquisition works for me, YMMV)
some people like the scoutmount thing.. just never appealed to me though
haven't tried the ghost ring yet, but probably will
I don't generally do high X scopes on lever actions, but would not hesitate to do so if/when it's the thing to do that fits the task (although cheekweld can be an issue, you have to decide for yourself)
probably not on the calibers specific to this thread, but never say never, a 45-70 can reach a long long way if loaded to do so
half the fun of owning a gun is trying out different setups