Sheo, that kit looks pretty decent, Leeda is a solid brand & yes, I've bought some of their stuff from Argos as well, for Sea & Pike fishing. Their neoprene gloves for £6-7 were excellent & half to a third of the price in many specialist shops & even on the net. I'm guessing the line will be pretty light & the reel basic but the rod itself will probably be ok. They know many folk will upgrade. I wouldn't go much above 15-18lbs & the lighter third of the weight range for long casting in an estuary/off the beach with that sort of kit but into deeper water from a pier or boat, you could probably go higher. 10' is a good size to start with as well, gives a decent cast without the handling problems of longer rods. Remember to take decent waterproof clothing/something warm as it can get surprisingly cold, quickly when you fish. At any spot you choose to fish from, look about, check tide marks & that there is clear access & that you have a good footing to cast from, you don't want to get cut-off or skite away when you cast. Use sunblock on bright days & moisturiser in rougher weather, conditions can get hard on the skin.
You would also be well advised to get an extra pack of lures/hooks/weights & traces as a beginner to sea fishing will tend to lose a fair bit of tackle & there is nothing worse than being stuck on the far end of a pier somewhere with your last weight on the seabed.

Other anglers are usually pretty decent about helping you out & giving advice tho, we have all been there!
One other reccomendation - with sea kit,
always use a swivel above your hooks/lures, if you don't, you will find-out about line-twist & birds-nestng
very quickly!
Lastly,
always remember to wash your rod, reel & any lures used after fishing, sea spray is
very corrosive & this is one area where budget tackle can suffer badly - Mine gets a good rinse in the shower & is then stood-up to air dry before packing away. Lures can lose their sparkle in just a few days if not washed.
Lidl are another good budget place to watch for sea fishing gear, their boxes of sea lures etc are pretty decent. I know I should say "support your local tackle shop" but I'm also well aware that many are rip-off merchants of the highest order & the antics of firms like Lureflash & Snowbee are making the local tackle shop as corporate as any other McBiz.

Still, if you find a good one, they are worth using for all sorts of other good reasons.
The Glasgow Angling Centre are a reasonable online store & are very helpful on the phone:
http://www.fishingmegastore.com/
Mullarkeys are also good & can be very cheap indeed for some stuff but it is helpful to know a bit more when dealing with them:
http://www.mullarkeys.co.uk/