Microphen, what is your preferred way of using it?

I plan to use Hp5+ in 35mm to do a little of project of mine in the zoo. Hp5+ will definitely need to be pushed to 800 at the minimum and maybe to 1600 (I have not pushed anything to 3200, I might have to). I bought some Microphen an it seems that this can be used stock, 1+1, 1+3 or even re-useable? Pros and cons of each? And is this similar to Xtol?

IIRC Microphen produces softer edges than XTOL. I moved to XTOL a decade ago.

Microphen makes sense when you push ISO400 to 1600 or 3200. In that case it's superior to Xtol IMO: it makes better tone and better grain after wild pushing.
For lower EIs it doesn't make much sense, as it always produces more present grain, and a starchy tone compared to MQ developers.
HP5+ is the most versatile film there is: think of it as several films, because it has indeed several grain sizes mixed. Its best image structure and controlled grain are made at 200 with Perceptol. With D-76/ID-11, you can use it at 400 and 800 with a bit more grain and a bit less definition than with Perceptol. And with Microphen it makes 1600 and 3200 good for wet printing, but with more grain and less definition, of course, than with standard developers.
I use it in several dilutions, but for pushing, stock is better. I wouldn't use it at 800 because at 800 tone and grain don't suffer with D-76/ID-11.
Microphen is wonderful when light is very low, like 1/60th f/1.4 at EI3200: then it's necessary.
In natural available light as in a zoo, I'd use HP5+ at 400, to record low contrast and sunny scenes without problem. Most photographs will be around 1/125 - 1/250 with f/5-6 - f/8.
That way you get better definition than with Microphen.
Another great developer for HP5+ is Sandy King's Pyrocat-HD, if you don't like grain: it paints what remained transparent in your negative, so grain is less visible, and it also makes a very sharp type of edges.
Personally I like the sharp small grain and the tone in Perceptol 1+2.
If you ever do the same scene at different EIs with different developers, you'll see the differences clearly when you wet print.
If you scan you'll see nothing but new digital photographs the scanner makes, and those vary depending on scanner and software.

You asked about reuse, etc.:
Ilford states you can reuse a litre of stock Microphen for ten rolls adding 10% development time for every next roll. Many photographers find that too much (high contrast) after a few rolls, so some users prefer 5%, and some others establish their own systems. There are formulas for replenishment too. I tried both -reuse and replenishment- and I didn't enjoy them, and I saw no real visual benefits. I like discarding what I use, even stock after the unusual push to 3200.
My personal use of Microphen some years ago, and my reasons for liking it, are different. I do three things with Microphen: I use it to get sharp present grain from Tri-X, so I push it to 1000 at 1+2. I use it a second way, though, for a different reason with TMY at 1000 too, also 1+2: grain is then much smaller than with Tri-X, and this is my most common use, for mixed scenes, so I use Microphen's speed and contrast control, to be able to get sunny scenes too, in the same roll, with decent shadows, because 1000 with Microphen is not a strong push, and TMY's film design is, for this, more appropriate than Tri-X, which at 1000 is better for overcast, but inferior for portraiture. The third thing I do is enhancing grain seriously for certain scenes without skin, with sodium carbonate added for higher temperature development, and it works with many films.
Don't worry if you don't use your Microphen for the zoo project: you'll find several different uses for it in the future.

Thank you for the information, I really appreciate it. Sadly the pictures will not be taken in well lit areas, most of it is of Hummingbirds at an enclosed aviary. I really do not want to use a Gimbal or a Tripod, pictures will be taken at f4 with a SS of 1/250th-1/500th of a second. No form of vibration reduction too but I have learned to use the surroundings as a brace. I have a couple of developers coming (R09 and Pyrocat HD), I will experiment with all of them. I will skip the re-use part of Microphen and just dilute it.

Oh, if light is not abundant, then of course you'll have to push...
Go for 1600 in Microphen stock if it'll be HP5+.
Remember that with the higher contrast it implies, exposure must be very accurate: overexposing is a little problematic, but underexposure is something you can't afford, because the right exposure at 1600 is already giving the film 1/8th of the light the film was designed for, as its real speed is close to 200.
Have in mind that if you attend your camera meter, you should give one more stop of light if half your scene is white, and two stops if white walls are most of the scene: just as a guide. And avoid light sources and windows to a zone with more light behind your scene, and that's enough to make most images work for wet printing in the future.
Finally, f/4 will give you very slow speeds in many situations... An f/1.4 lens will save your day no doubt: it can give your film eight times the light f/4 can.
Good luck !!!