Hi there, and welcome to p99.
1) the pet robs you of xp if it out damages you, but seeing as sk pets are pretty much the worst acting DoT you'll cast this won't be much of a concern. Also, some of your DoTs (disease cloud is the one) will get you aggro like no one's business. So whatever it is you sent your pet on will immediately come to you. Your pet will thus be alive for a good number of fights, and you'll be the one tanking.
Whether or not to cast pets will depend on your situation, and you'll figure things out as you level. You'll want a pet in outdoors areas where you'll be fear kiting or if you're about to fight a SK mob, so it'll eat the harmtouch. He'll provide some damage but won't be able to out damage you.
That being said, in dungeons you might experience pet pathing through walls or aggroing EVERYTHING (it'll be very low level compared to what you're fighting as you continue to level so they'll aggro low level mobs that wouldn't aggro you). Also if you're grouping with a CC class (bard/chanter) and your pet is beating up on things they mezz they will be very upset with you when the thing breaks mezz and starts beating up on them. In a group situation DPS is not a job you'll be doing so the low numbers the pet puts out will likely not be necessary.
2) shield is always great to have, it'll help you with your main job: tanking. your clerics will thank you down the line as shield ac is always going to provide solid damage mitigation. Not to mention your shield bash will be excellent for interrupting casters and also making that great shovel hitting skull noise.
you'll want to work up all your combat skills of course, just in case you get some neat toys to play with (your epic for example is a 2h slasher, but there are reasons i've not seen as many on the server). Plus with double attack a solid 2h weapon will make satisfying crunching noises on your opponents
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As far as decent starting weapons you might want to look at
Sword of Skyfire,
Firerune Brand /
Blade of Xalgoz,
Enameled Black Mace, or any cheap decent ratio'd things coming out in large amounts from Velious. Stay safe out there, and good hunting.