Welcome to the forum...

Any idea why the pond seems to only have stunted bluegill(BG) and bullheads and nothing else? Are you sure they are in fact BG and not another sunfish species like green sunfish(GSF)? GSF and bullheads are very winter kill tolerant so that is my concern. The fact that the pond is 25 feet deep should help lessen the risk of winter kill, but it won't guarantee it. Are you sure the pond is actually 25 feet deep? I would not trust what others have told you, as I have found they almost always over estimate the depth...

If you are not sure how to ID BG and GSF, take a photo of a half dozen or so fish and post the photos on here. If you are not sure how to post pics, check the archives section and there is a nice post on how there. Speaking of the archives, check out the information there are growing large BG. There is lots of great information there... Are you mostly concerned about your BG in the pond, with less emphasis on the LMB? If so, you want to stock around 75 LMB in the 6"-8" size range. If you are more looking for a balance between the two species I would recommend around 25. It will take a while to control the BG and it may be an almost impossible endeavor. Northern ponds where BG have gotten out of control can be very difficult to get back into balance.

The simple fact that your pond may go to 25 feet deep doesn't mean it will hold trout year round. Unless aerated, much below 10 feet or so will be void of dissolved oxygen and will be dead to fish life. If you aerate, the pond will be more oxygenated but will likely become too warm for trout to survive. If you had a large spring feeding your pond, then there is more of a likelihood rainbows could survive. The same would hold true with well water, however that would require a very large amount of well water to be pumped. There is always the option of seasonal trout stocking which is what many members on here do. You stock the rainbows in the fall when water temps reach the 60's. You enjoy them through the winter and then fish them out by late spring before the temps get too high for them. If you do stock some rainbows, I'd go with as many as 75 for a spring stocking or 150 for a fall stocking. The more you stock, the more you'll need to be eating rainbow trout for dinner.

This late May or early June, try to do a seine survey... Purchase a 50'x4' seine and locate an area of your pond where the slope is a little more gradual and there is little obstruction. Run the seine there and see what you catch. Utilizing this data can really tell you a lot about the balance of you pond... The placing of simple minnow traps can also tell you some.

Good luck!