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Being the idiot I am, I used to regularly cycle through sea water and not wash my bike. The nipples on the Spank Oozy 345 wheelset corroded and started falling apart. A while back a wheel builder told me they were a waste of time to fix because wheel-builder-reasons but I spent a lot of money on them so intend to fix them myself now. I'm a noob at this though.
Wheelset are Spank Oozy Trail 345. Spank chart says spokes are (straight pull) 2.2/1.8/2.0, and nipples are 'Alloy DSN Nipples' and explains "Longer nipples with 4mm square drive head"
Here's a pic:
I've not measured them yet. I keep meaning to. But anyway. I think they're mostly gone so might as well replace the whole lot.
Don't really want square head as requires another tool. I've got the regular driver. Was thinking brass but coastal rides less frequent. Brass stronger though, and wheelbuilder said issue was in part due to wheel design and the angles of the spokes going to the rim. Nipples that are happy at greater range of angles?
Other than dimensions G Z D in the above image, is there anything else to watch out for?
Those ACI Alpina nipples on CycleBasket are appealing price-wise. Are they of suitable durability for 30mm MTB rims?
Also what's a good cheap option for clamping straight pull spokes, might try DIY, can't find anything cheap to purchase. Thinking drilling a small hole between two sheets of 3mm plastic and attaching to molegrips (somehow).
As far as I can tell, the rims spoke bed is pretty flat and the drillings aren't offset.
If nipple angles are extreme then building with Sapim/Newman MG washers would be a good thing.
These may also allow for switching to a regular style nipple and keeping current spokes as they will add 2mm to the spoke length, so your current spokes may already be a little longer than a calculator would give you for regular nipples..iirc DT's calc adds some spoke length for their squorx nips.
Those aci nips don't look like they'd do well with "extreme" nipple angles due to the shoulder.
Sapim polyax (brass available) nipples with the MG washers to mitigate the angles your wheelbuilder mentions, however I've had good success with DT's nip profiles in MG washers too. 
Tools wise, using the flat section of needle nose pliers after the cutters before the real jaws is good. Fingers get tired pretty quickly otherwise. Don't underestimate ow quickly you will burn through anything you wrap over tools though.. inner tubes, electrical tape, silicone backed emery cloth.. tried loads but metal on metal is fine with care.
If you're doing new spokes.. Sapim D Light - every day. Comes with wrench flats by the threaded end so you can use a small adjustable spanner to prevent the spoke turning/winding up.
(casual wheel builder)
I've used sapim polyax brass nips with spank spike race 33 rims, the spoke holes aren't offset but I've have zero issues and the build was hassle free too.
@endomick interesting. And they look better priced than some.
This the thread I made over a year ago.
https://singletrackmag.com/forum/topic/spanked-straight-pull-content-advice-please/
@bearback thanks also for the info, needs more digesting... It's all a bit daunting to know what's best to do.... especially while trying to keep costs down.
I can't decide whether to try to get these wheels up and running first or a 26" UST straight pull wheel to make a 2nd hardtail commuter lol. Decisions.
Here's a video on youtube for a DIY spoke holder.
I bought a cheap (Draper branded) cable pulling tool for £10 and sawed some of it off, and drilled and screwed two parts together so it acts like the £40 Park Tool jobby.
It's OK, does the job, but not overly comfortable, and combined with using the Park Tool Y shaped tool (for the square driver) is a bit fiddly.
Here's a pic of the old nipples.
The nipples look to be 16mm. The Spank chart lists them as DSN nipples - would that just mean Double Square Nipple?
So if I were to go the route @bearback mentions, using washers (2mm deep) I'd go for 14mm nipples?