I concur w Danksta's post. Some addl thoughts:

A. You can spec attribute points one time and be done. Honestly, they can all go into magic or stamina for any character. Ten attribute points in health is worth 1150 max health. This is close to one health enchant on a piece of armor. So I find that it's way easier to balance max stam/health by changing out armor enchants if need be, although as a DK you're going to invest in mostly stamina in both attribute and enchants.

Champion points are a different matter. There are certainly specs that work great for both so you never have to change. You'd be a "B+" pvper/pve-er. But to be the "best," they likely do need a little tweaking between pvp and pve. But you really don't need to tweak until you get higher in CPs.

For now, I advise spending in a few very strong CP items. In green, invest most in stam recover and stam cost reduce (warlord). You're working toward 120 in lover, w like a 85/25/10 spread in resource recovery, then all other greens in warlord. In blue you're all about the ritual, with most in mighty for now (increasing power of EVERY stam attack). My end game is 90 mighty, 50 precise strike, some piercing and thaumaturge w a few in blessed. In red you should race to 120 in the lady w an even spread in hardy and element defend. These reduce incoming magic and stamina attacks...they are the best buffs in red. Of course, for pvp you might want resistant - only human players crit. But focusing on the others first is probably wise, they give you good all around resistance.

B. As Danksta says, there are enough skill points in the game to open most of the skills. My main has all of the craft skills and passive, almost every ability he would want, four weapon lines, two armor, and tons of auxiliary stuff. However, I've played him for two years, and a lot of skill points are a pain in the arse to get. To get his points, my main got every sky shard and played every skill point quest...ugh.

I highly advise creating two addl crafting toons - one for smith, cloth and wood, then a second for alchemy, enchant, provision. Have your main adventure and pick up stuff...he'll get high level items. You can push items to your bank to deconstruct, and they can hold/manage all the junk. If you're going to craft armor sets, get your guy researching asap. It takes about a year to get all nine traits on every armor piece. (ESO workbench is a great iOS/android app to assist).

And hey, maybe you'll want to play a Templar/sorc/nightblade/magic dk some day - having secondary craft characters starts the leveling on these so if you ever want to try one, you don't have to start from scratch. Whether you use your main or secondary toons, you need about 66 skill points to be a trade crafter and 50 for the consumables (skipping junk passives).

C. I don't know the current stam tank meta. Deltias gaming is a good resource...he explains a lot in his videos, which might help you learn what certain Passives/skills/etc do.

D. If you mean top pvp-er as in "on the leaderboards," sure. You can earn enough AP to get up there. If you mean top as in "I win 95% of the fights I get into," then probably not. Being down 400 champion points is significant.

I agree with the approx 15% handicap estimate. But don't worry, you'll grind them up. Use your daily enlightenment (it saves up for 12 days worth, btw). And make sure to level lots of skills when enlightened. You have another 100 CPs that accumulate fast, then 250-350 is a little slow, then beyond that you're looking at weeks of playing, not hours, lol.

You can't do anything fast about the CP handicap, but there are other handicaps you can work on. Are you using the best sets for your build? Once you have two 5-piece sets, should you go get a monster helm set? (any that cause damage appropriate to your play style are very helpful for a DK) Are you using purple armor instead of gold? That's a 20%ish handicap. Is the armor enchanted appropriately? You probably want mostly stamina enchants, maybe a few health, and almost definitely weapon damage on the jewelry. Are you using rally/forward momentum every 30 seconds? You need the major brutality 20% damage buff. Do you know your other skills backward and forward so you can equip the right tools for the job, and are those skills leveled?

While you're working toward all of that (behold the ESO grind, lol), you're not going to be an unusable character...it just means playing the content a little different. In pvp, you're not going to be able to 1vX much since you won't deal a lot of damage. But you'll still be tanky as heck. Run in a small group w other classes that can dps. Turn on your combat text and start learning how to deal more/better damage. Learn what's hitting you hard and how to mitigate it. In PVE, start running maelstrom. If you can't do vet yet, do the regular, you'll earn a lot of xp and learn a lot. Start running vet undaunted dailies in a group, and when able start running regular undaunted dailies alone. (You can't complete all of them...some bosses have snares that prevent solo completion, but many are doable, and you will become a far better player running these).

Hope that helps. If you have any other questions, feel free to message me any time. I have a "leveling guild" where we try to assist new players with some of the complicated play and leveling mechanics...always happy to answer questions.