The JR pass is only worth it if you travel through different cities, if you are just travelling to Tokyo to Kyoto for example, I would just pay on the Suica. You can do the online calculator or just use google to calculate which trip is easier - paying individually on Suica or getting a JR Pass.
Smart cards like Icoca, Suica and Pasmo are generally valid across Japan, so don't worry about which one you buy. You can use Icoca/Pasmo/Suica for all trains, subways and buses in Osaka.
The only difference between PASMO and SUICA is who sells them. SUICA is from JR East, and PASMO is from Tokyo-area non-JR rail operators, including Tokyo Metro and Toei Subway. Wherever you can use SUICA, you can use PASMO, and vice versa. Same with charging with new amounts.
Yes, it can. Suica cards can be used anywhere the Suica IC card logo is displayed. It can also be used in convenience stores and vending machines outside of the Tokyo area. You cannot use the Suica to travel between Tokyo and Osaka, but you can use it to travel within cities such as Osaka and Kyoto.
Where to buy a My Suica card? You can purchase a “My Suica” at any JR East station ticketing machine or booth, including the ones located at Narita and Haneda airport.You can also buy it at some tourist information centers.
The Welcome Suica is the same same tap-and-go travel card and has the same functions as the standard Suica card, but there is no need to pay the 500 JYP deposit in advance.
You can charge your Welcome Suica card (put money on it) in various places, including ticket machines at stations and in convenience stores. Just look for the mark. You can charge your card with cash. You can put up to 20,000 yen on it.
You can check your balance (the amount left of the money you added by charging) at ticket vending machines, multifunctional ticket vending machines and charging machines in the Suica area. Your balance is also displayed on the ticket gate when you pass through.
If you calculate that your travel costs will be lower if you buy individual tickets for each journey, then it's not worth buying a JR Pass. However, if you take into account journeys on Shinkansen high-speed trains or other means of transport, the savings you make become substantial.