I'm putting together an ultralight to fling small jigs, grubs, inlines, and maybe jerkbaits for crappie, trout, and the occasional dink/finesse bass. My idea is to buy 7 foot Fenwick Eagle and a 3000 Pfluger President, put the President on my bass rod, and move its cheapo Speed Spin to the Eagle. 

 

Only downside I'm aware of is that it'll take a crap ton of line to fill the spool up, but that's solved by buying some crappy Walmart line to use as backing. 

Not stupid at all. Maybe the reel might be a little heavy but it will work with the bigger spool you can get away fishing with floro?

Besides it feeling awkward it won’t affect anything

Welcome aboard!

 

You'll only know if you try it out   There are no rules

as to what you can put on a UL rod. Well, almost none...

Depends how long the rod is a 7' ultra light may feel perfect with a 3000 size reel 

But a 3000 reel will feel awkward on a 5' ul and the stripping guide wont match  the spool diameter  coming off the reel for casting

Its not that bad since the rod is 7'. 

It would feel very unbalanced if it was 6'6

It's a bit large for my taste, but there is certainly nothing wrong with it.  As long as the rod's guide train isn't a hindrance, which it shouldn't be, especially with the limber lines used on UL gear, you may get a tad more casting distance with the larger diameter spool.

 

At worst, you fish the UL with the larger reel until you have some extra cash for a suitable 1000 or 2000 sized reel.  Who knows, you might just like it with the 3000.

If the 3000 is not too heavy, it will probably be alright. A larger spool should also help with casting farther if necessary with less effort and enable you to hold a lot of line, which is something I like to have in spades. I like the idea!  True UL reels like in the 1000 size don’t suit my needs or conditions. 

Everyone is going to have a different opinion- give it a try and see what you think!