By "manual" do you mean manual exposure or manual focus? Almost all of today's auto-focus cameras can be switched to manual focus and/or manual exposure. All you absolutely need is shutter control, aperture control, and a meter; everything else is cake. Tell us what you want to shoot, and we could recommend features you might want.
A bigger neg holds more info and decreases the the amount of enlargement necessary (or increases the amount of enlargement possible). An 8"x10" piece of paper is over 50 times the area of a 35mm neg, but only four times the area of a 4"x5" neg. The MF sizes fall between these (6cmx4.5cm, 6x6, 6x7, fuji makes a 6x8, 6x9, 6x12, and 6x17cm). If you compare an 11x14 print from 35mm with the same size print from a larger format you would probably notice increased sharpness and decreased grain in the MF/LF print. I've noticed that it's a lot easier to get a really nice tonal range and contrast from a bigger neg. I've goofed on exposure and still been able to get a nice print from some of my MF/LF shots, and I know I would have struggled with it in 35mm.
If you think of the cost in terms of per shot, then yes MF and LF are more expensive. But if you think of it in terms of square inches of film then a roll of 120, a 36exp roll of 35mm, and 4 4"x5" sheets of film are the same. I get Tmax 100 120 size for $2.15 a roll and 4 4x5 sheets of Tmax 100 costs about $3.20. I haven't bought a 36exp 35mm roll of Tmax 100 in a while, but I'm guessing it's in that same price range.
The equipment does tend to cost more, but it's typically considered "pro" equipment, and there's plenty of really expensive "pro" 35mm gear. Right now on
EBAY basic Hasselblads are going for about a third of what they were worth when I last looked a few years ago. You can get a good used MF camera for the price of a mid level consumer 35mm AF SLR. You can find decent working used MF and LF cameras for $100 if you just want to dip your toe in first. Yashica TLRs for MF and less popular models of the Speed Graphic for LF is where I'd look.
I think that one big disadvantage of MF is equipment size. The cameras tend to be big, heavier, and just generally not as nimble as 35mm gear. Some models can be hand held successfully, but many will do their best work on a tripod.
When I look at my work I think it's easy to see the difference between 35mm and MF/LF in prints as small as 8"x10". But there are folks who have the gear and the technique to get shots with 35mm that I'll mistake for a larger format. So consider your maximum print size. If you're never going to make prints bigger than 11"x14" then good 35mm equip and skills and a light load may be a better choice than bulky MF gear. I get a masochistic thrill hauling a heavy tripod, camera, and film around.