Updating photo management strategy with add'l laptop?

Question

Hello -
I have added a new MacBook Air to a set of computers - old MacBook, older iMac.  The iMac hard drive bit the dust earlier this year so it has a brand new 750 GB hard drive with Mavericks installed.  That's the background to wanting to updating my photo management / storage strategy now that I have an additional computer.
I keep my iPhoto library on an external drive connected to my desktop (the iMac) and have since the beginning - that baby is about 350 GB and isn't updated b/c now I've had photos on the Macbook and don't want to get into the same habit with the new MB Air.  I take a lot of photos, decent amount of video but it's all personal, not my profession.  My camera shoots with 10 - 15 MB size per photo though, so it adds up.  I use SmugMug to share my photos (and online backup strategy) - the process on a good day is to pull the photos off my camera, do any editing, upload the ones I want to share to Smugmug, then save/store the originals.
I'd like to consolidate now that I've got a new computer in the mix - and storage drives keep keep getting bigger and less expensive. ;-)
My current thinking is to get a NEW big external storage drive and set it up to be ONLY a repository for photos and video.  I'd likely use that storage drive with a main iPhoto library (or whatever software I use) on the desktop, especially since it's now on an updated OS.
What I'm debating is whether I should go with the larger storage of a desktop storage drive - or go with the portable with the largest storage capability just in case I *ever* want to take it and use it with the laptop (now or in the future)?
Does that seem like a sound strategy?  Thoughts?  Thanks!
P.S.  A good thing to add is that the iMac has only Firewire 800 available, unfortunately (and USB obviously).  The MacBook Air has thunderbolt.  If I use a Thunderbolt storage drive on the iMac it would need a converter (which I think will slow it down - but is that slower than the usual Firewire 800 speeds?)  If I use a Firewire 800 storage drive with the iMac, I'd need a converter if I went to use it with the Macbook Air - not ideal, but not going to happen very often. 

Answer 1

1. You need two drives: one to hold the Photos and one to be a back up for that.
2.
What I'm debating is whether I should go with the larger storage of a desktop storage drive - or go with the portable with the largest storage capability just in case I *ever* want to take it and use it with the laptop (now or in the future)?
Well, as you need both, I'd get one of each, and keep the portable outside the house - even in your car.
SmugMug is excellent as off-site storage (as is Flickr) for your photos. But if whatever you choose to manage your apps has a library of any form, then you need to also back that up. And everything pretty much uses a Library - Picas, iPhoto, Aperture, Lightroom etc  - of some form or other.
The thunderbolt to Firewire adaptor will not make an appreciable difference in performance. But frankly, I'd go for USB, I'm not sure of the long term prospects for Firewire.