Chilies are dried before grinding. There are several ways to dry them:

• Leave them in an exposed part of the fridge for several weeks. There should be a lot of open air around it, to allow moisture to escape.
• String them up outside. To do this, poke holes and run strings through them and tie the strings up so they're spread out. For best results, you should do this during hot, dry weather, and ensure they get plenty of sunlight. Expect it to take several weeks.
• Oven-dry them at low temperatures. You want temperatures to be under 150°F/65°C so as not to cook them, and it will take several hours to a day or two. Reduce the temperature if you see the peppers darkening or turning black. Rotate the peppers regularly to allow even drying, and leave the oven door slightly open to allow moisture to escape. If you wish to have a little more roasted flavor, increase the temperature.
• Use a freeze-drying machine or dehydrator.

Discard any peppers with rotten spots, both before and after drying. Before grinding, remove stems and seeds.

Grinding: I've successfully used a blade-type coffee grinder to grind dried peppers into flakes. A blender or food processor should also work, assuming you are handling larger quantities. I must confess puzzlement about what exactly a "mixer-grinder" is, even after consulting the link. I believe the appliance may not have an exact equivalent in Europe or the United States. However, if it is suitable for blending or grinding it should work fine for dried peppers.

I should add that you ought to wear gloves when handling the peppers, and beware of the fumes from the dehydrator or oven, as they may be very pungent. In extreme causes, protective goggles may be a good idea.

No one device, manual or electric, is ideal for all of the tasks that you have enumerated. Many cooks will have more than one tool, depending on the job at hand.

Some spices, particularly cinnamon, are very difficult to grind effectively at home without leaving fibrous bits that may give an unpleasant mouth feel. Of course, when infusing flavor from a whole stick of cinnamon, this is not an issue.

Bottom Line

I would recommend having at least a Microplane type grater for ginger, garlic, and so on, and a rotary type electric grinder for most hard spices.

For the specialty task of making peanut butter, a blender is probably your best tool.

Morter and Pestle

Also known as a molcajete, is probably the most versatile, but most labor intensive spice grinding tool.

• Can grind, mash, or mix both dry or wet items, so it is suitable for garlic and ginger; still it is most effective on very hard, frangible spices which can be crushed, or soft items like garlic which can be mashed. Fibrous spices like cumin can be very difficult to do.
• Lots of work
• Only suitable for small quantities

Microplane style grater

A grater with very fine, usually etched, openings is suitable for some tasks including:

• Garlic, gingner, galangal and the like
• Nutmeg

Nutmeg Grinder

A specialty item, just for nutmeg. Most nutmeg grinders actually make very fine shavings, but it is essentially the same thing. They also have storage for nutmegs.

Blender

Electric blenders are suitable for some grinding tasks:

• Making peanut butter
• Grinding soft spices or making wet spice mixtures, as with garlic, ginger, capiscum type peppers

Some high quality blenders may also do a decent job with softer seeds like cumin seeds.

Electric rotary grinder

These are often marketed as coffee grinders, but they are extremely effective as spice grinders—however, due to lingering flavors, you want to devote one to either coffee or to spices.

Suitable for dry spices, such as cumin, black pepper, allspice, mustard seeds, and so on.

Not very effective for the hardest spices, such as cinnamon.

Note that clove oil (also found to some extent in nutmeg) can cloud plastic parts over time.

Pepper Grinder

As the name implies, ideal for black pepper, but also effective on other small spices that can fit through the mill such as mustard seeds. Also provides a small quanitity of storage. Most permit the grind size to be adjusted.

Specific Questions

Which kind of grinders allow water in them for making a paste of the spices?

Mortar and pestle, and blenders are suitable for pastes. However, you can also grind your dry spices, and then add them to a wet mixture to create a paste.

Is there some maximum and minimum capacity for each of the type of grinders?

Most home style devices are suitable only for very small quantities. The nutmeg and pepper grinders are good for teaspoon type quantities, and rotary grinders up to a few tablespoons.

Blnders have much higher capacities, but may not be effective except with very soft or frangible items. Peanut butter is one application that they do well with in larger quantities.

What are the types of manual grinders which do not require too much amount of manual power/effort?

They all require significant effort. For spices used in very small quantities, such as black pepper, that may not be noticeable.

Which kind of grinders allow us to have a fine powder of spices rather than bits?

None of the home methods will produce the very fine, even powder that you might expect from a commercial spice house. They have extremely high quality, sometimes specialized equipment, and they also sieve or screen the resulting product to ensure it is uniform, and to exclude larger bits.

Some spices are more suitable for home grinding than others. Ones that you should have little trouble with include black pepper, nutmeg, allspice, mustard seed.

Spices that are very difficult to grind at home include cinnamon.

Cumin, one of the most popular spices, is easy to grind, but difficult to get a perfectly smooth and uniform powder. It tends to have little threads and fibrous bits. In many applications this is not noticeable.