Well there are some issues you need to consider here, perhaps you have already thought about all of these things but perhaps not...
1. Shrimp add very little to the bioload; if it was a shrimp only tank that size you could easily have 500+ shrimp in there. Given you have fish in the tank, how many shrimp you can have is going to be determined by how many fish you already have. If you are already at the point of the tank being "maxed" in terms of fish, then I would suggest not more than 50-100 shrimp. If the tank is understocked with fish, then several hundred shrimp would be fine.
2. Partially related to point #1 above, dwarf shrimp tend to be much more sensitive to water paramenters (ammonia, nitrite, nitrate) than even "sensitive" aquarium fish. *Any* ammonia or nitrite, no matter how little, will likely wipe out your shrimp in short order, and even nitrate levels that would be perfectly fine for a fish tank can kill off shrimp. If you are serious about keeping shrimp in this tank, aim to keep nitrate levels at 5 ppm or less.
3. If the fish are no larger than zebra danios, then (assuming they are peaceful fish), adult shrimp will be fine. But don't expect any babies to survive unless you are very thickly planted with large quantities of java moss or similar types of moss for the babies to hide in and feed without becoming food for the fish.
4. That being said, even adult shrimp will usually not exhibit their full range of behaviors (including most of their playful antics) if there are any fish in the tank. In combo fish/shrimp tanks, my experience is the shrimp spend nearly all of their time hiding, or foraging only in the most heavily sheltered parts of the tank. Whereas in a shrimp-only tank, they are far more playful, more open, and will spend time throughout the whole tank, the entire bottom, sides of the glass, crawling all over plants & driftwood, even swimming to the surface and "hanging" upside down to grab flake food off the surface of the water, etc. Basically, a lot of the behaviors that make dwarf shrimp so much fun to keep you will either not see at all, or else see very little of, if they are in a tank with fish.
5. Not all dwarf shrimp prefer the same conditions. Some need hard, slightly alkaline water (e.g. most of the
Neocaridina such as Red Cherry, Yellow, and Snowball), some need very hard, highly alkaline water (e.g. the new Sulawesi shrimp), while others need soft, acidic water (e.g. Crystal Red, Tiger, and related shrimp). Dwarf shrimp are quite capable of adapting to large extremes when it comes to temperature, but pH and hardness are quite important if you want healthy, thriving shrimp--and even MORE important if you want your shrimp to breed. So before you go buying any shrimp, make sure you know what pH and hardness your tank is at and buy shrimp appropriate for those water conditions. And when it comes to what conditions what shrimp need, go to a trusted hobby site (something like
Petshrimp.com -- Freshwater Shrimp Hub of the world) rather than the website of the place selling you the shrimp, as many of them (to be blunt) will lie and tell you "this species will do great in all water conditions, whether acidic or alkaline, hard or soft" etc. Don't believe it! *Almost* all dwarf shrimp have a preference one way or the other (hard alkaline or soft acidic), and while you might get them to *live* in non-ideal conditions, they will have shortened lifespans, be less energetic, and breed very little (if at all) if conditions are not to their liking. Yes, there are a few exceptions (the Amano shrimp seems to be one of them), but the exceptions are rather rare. Also note that some need brackish water (e.g. the Hawaiin Red), and others while living in freshwater require brackish water to breed; or more correctly, newborn larvae/shrimplets will die unless they are in brackish water (the Amano is an example of this).
6. Many dwarf shrimp species are known to be able to interbreed; others are suspected to (but have not had rigorous testing done). Interbreeding will result in hybrids that are almost certain to be naturally colored (drab brown usually) which are both ugly and of no use to the hobby in terms of continuing carefully bred & selected strains. In order to avoid that, I would suggest you pick only one (or at most two) species of shrimp and stick with those. Unfortunately, it can be difficult to accomplish both #6 and #5, since (in general) the types of shrimp that prefer the same water conditions are also the types of shrimp most likely to interbreed.
Dwarf shrimp are amazing little things. But as someone who has kept them in community tanks as well as in shrimp-only tanks, I can only say that it wasn't until I did the latter that I truly fell in love with them. It makes ALL the difference in the world to have them in a tank of their own. So if you are serious about keeping these guys and you have the room for it, I'd suggest another tank.