I just started a SD/DM character myself and my playstyle matches yours pretty well. I am by no means an expert on Tankers, as my soloing nature pushes me more towards scrapping, but this is what I came up with.
Hero Plan by Mids' Hero Designer 1.401
http://www.cohplanner.com/
[u]Click this DataLink to open the build![u]
Level 37 Magic Tanker
Primary Power Set: Shield Defense
Secondary Power Set: Dark Melee
Power Pool: Leaping
Power Pool: Fitness
Hero Profile:
Level 1: Deflection -- Empty(A), Empty(11), Empty(15), Empty(23)
Level 1: Shadow Punch -- Empty(A), Empty(7), Empty(9), Empty(11), Empty(13)
Level 2: True Grit -- Empty(A), Empty(3), Empty(3)
Level 4: Shadow Maul -- Empty(A), Empty(5), Empty(5), Empty(9)
Level 6: Active Defense -- Empty(A), Empty(7)
Level 8: Against All Odds -- Empty(A)
Level 10: Battle Agility -- Empty(A), Empty(13), Empty(15), Empty(23)
Level 12: Combat Jumping -- Empty(A), Empty(25)
Level 14: Hurdle -- Empty(A)
Level 16: Siphon Life -- Empty(A), Empty(17), Empty(17), Empty(19), Empty(19)
Level 18: Health -- Empty(A), Empty(34), Empty(34)
Level 20: Stamina -- Empty(A), Empty(21), Empty(21)
Level 22: Super Jump -- Empty(A)
Level 24: Phalanx Fighting -- Empty(A), Empty(25)
Level 26: Shield Charge -- Empty(A), Empty(27), Empty(27), Empty(29), Empty(29), Empty(36)
Level 28: Soul Drain -- Empty(A), Empty(31), Empty(31), Empty(31), Empty(33), Empty(33)
Level 30: Taunt -- Empty(A), Empty(34)
Level 32: One with the Shield -- Empty(A), Empty(33)
Level 35: Dark Consumption -- Empty(A), Empty(36), Empty(36), Empty(37), Empty(37), Empty(37)
Level 38: [Empty]
Level 41: [Empty]
Level 44: [Empty]
Level 47: [Empty]
Level 49: [Empty]
------------
Level 1: Brawl -- Empty(A)
Level 1: Sprint -- Empty(A)
Level 2: Rest -- Empty(A)
Level 1: Gauntlet
In YOUR build I would definitely move Active Defense up quite a bit as you can't Taunt (or anything else) if you are mezzed.
For the taunt question there is no solid answer. Some people swear by taking it early while others say there is no need to take it until later, if at all. Play style will determine this for you. You can have two builds so try one with out taunt and see if you find your self wishing you had it, reversely try a build with it and see if you ever actually use it.
Thanks for the advice. I tweaked your build a bit, forest, but I'm doing something very similar, getting Active Defense sooner and I'm bumping stamina back down to 20.
Playing solo or grouped at 13 my biggest problem is endurance and to a lesser extent accuracy. I want to know if I should start buying/making some cheap endurance reduction IO's soon or save up my money (I've only got about 50k saved up so far, so it won't go very far!).
Endurance and accuracy issues will plague you until 20 (Stamina) and 22 (Single Origin enhancements) ... this is every Tanker's burden to bear.
If you can tough it out, I'd save your money for SOs at L22, being a new player.
SD/DM is a great combination btw. Mine is currently L20 and is really starting to shine. 
Hi, I'm a long time CoH lurker that is finally finding the time to play a character, hopefully through to 50. I was looking for a little bit of help building a decent, if not uber, character. Basically what I'm looking for is some advice on skills to take, a strategy for slotting things out that takes into account a bank starting at 0 and any gameplay tips that people might have for a first-time player who likes to min/max a bit. My playstyle is a mix of solo and team play -- ideally I should be able to do both well. SD/DM seems to be good for this: good taunting/defense for playing tank along with good enough damage that solo'ing isn't painful. Correct me if you think that's wrong! :-)
Here's the build I was looking at:
1 -- Shadow Punch
1 -- Deflection
2 -- True Grit
4 -- Smite
6 -- Battle Agility
8 -- Against All Odds
10 -- Combat Jumping
12 -- Phalanx Fighting
14 -- Super Jump
16 -- Siphon Life
18 -- Hurdle
20 -- Health
22 -- Stamina
24 -- Active Defense
26 -- Shield Charge
28 -- Soul Drain
30 -- Boxing
32 -- Tough
35 -- Dark Consumption
38 -- Midnight Grasp
41 -- Weave
44 -- Taunt
47 -- Grant Cover
50 -- Hasten?/One with the Shield?/Touch of Fear?
There are several powers I'm wondering if I should pick sooner or add. For example will I feel like I'm not useful enough in groups without taunt until 44? Contrariwise should I skip it altogether? Is Touch of Fear something I should be adding in earlier?
I'd be really grateful if someone could give me some advice on where to get started with IO's. For example if I could pick out some cheaper IO's to try and get around 25-35 that would be awesome. And do you think I should bother with SO's at all or just save up for IO's given that I won't have a lot of Influence to throw around?
Thanks for taking the time to read this and for any feedback!