Boris,
1) There are a few shops around Dublin that sell bait.
Personally I use a guy in Ringsend called Dave Tilly, a very helpful guy and usually great bait, send me a pm if you want his phone number.
Or I use Viking tackle in Bray, google it and you will get there number, again very good bait.
2) If we knew the answer to that we wouldnt need to fish anywhere else, but if your just getting started the east pier (the one with the light house) in Wicklow town is a great place to start, you catch plenty of fish and a good variety, but rarely any monsters.
3) That rod would be ok for fishing just over the side of the pier, using small weights approx 1 oz, with size 4 or 6 hooks and small baits. The bigger the weight you use, the stronger line you need. Line will be rated in lb's of strength, the standard sea fishing line would usually be around 15lb, but it does vary based on where you fish, and what fish you are trying to catch, but 15lb is a good starting point.
4) The benefit to fishing 2 rods, is that you can fish one in close, and 1 a bit further out, I tend to fish one in close with small hooks and baits, and 1 rod further out with bigger hooks/baits, obviously you can use that rod for fishing with feathers for mackerel, but they will be gone soon enough.
Your set up sounds ok to get you started, but there are some complex "rigs" (thats what you call your end bit of tackle) that can be used to much better effect once you have gained a bit more experience.
See this wesite link for rigs that can be built at home using different bits of tackle.
http://www.gemini-tackle.co.uk/rigs.htmlIt would be very helpful for you to get out with a few anglers off the site here who will be able to give you a first hand view of how you can broaden your skills.
I only started sea fishing last year, and meeting a few lads from the site here was extremely helpful when I was starting out.
I hope the above gives you a bit of help to get going.
There are also some useful tips on the site here regarding bait, tackle etc.
http://sea-angling-ireland.org/rods.htmhttp://sea-angling-ireland.org/bait%201%20-%20lug.htmhttp://sea-angling-ireland.org/map%20of ... 0shore.htmhttp://sea-angling-ireland.org/specimen%20list.htmThis site is great for helping you to identify species of fish that you may catch, whilst its a UK based site, many of the species of fish are present in irish waters anyway
http://web.ukonline.co.uk/aquarium/index.