Crossover questions First time Rig

Hi guys,
I have a project to build a small stack comprising of 2x MHB 4818 and one MT-130.
This is the first rig I will be building and although I have managed to collect a lot of info from reading forums and such I still have a few questions in regards to Crossover and filtering.
First off details:
I will put RCF LF18G401 drivers in the MHB 4818s
For the MT-130s I will put Precision Devices PD.121 for the mids. I am unsure which Compression driver would be best for the highs, the plan suggests BMS 4550 is this the best?

I need to know where to cut off my RCF lf18g401s and where to cut off my PD 121s. How will I do this? Passive crossover or active? Bearing in mind I would like this system to be as evolveable as possible (is that even a word?) haha
Also the BMS 4550 say they have a nominal impedance of 8 OHMs does this mean I cant wire it up in series with the PD 121? Does that mean 3 amps? Or 2 amps.
Which brings me on to amplification. Which amp would be best for this job, how many do I need?

It's a lot of questions I know ^^ I hope it makes sense. I am very eager to learn so any advice would be greatly appreciated!!
Also If you could tell me why you give me a specific answer so I can see how you worked it out and learn more from the experience that would be great!

Thanks guys! Looking forward to hearing from you.
Peace!

You cannot run the BMS 4550 in series. You and run 2 amp = 1 for sub,s and amp 2 = 1 channel for 121 and 1 channel for the 4550 .remember you will need a 3 way crossover.

Thank you for the response Do you have any recommendations for which amps and crossover? I heard there are amps with inbuilt crossovers do you have any experience with these?

Get yourself a speaker management system, a Behringer ultradrive or a dbx driverack pa plus are very good for the price £200 - £300, if you buy one from the offset you wont go wrong, standard 3 way active crossovers are ok but very limited compared to the above, good luck with your build buddy.

Thank you! So just to make sure I have understood, I would have this before or after the amp in my chain? and I would use this to select what frequencies go where is that correct? (sorry for newbie questions) and if i had the Behringer one I can use that as a limiter also? so all I would need in my hardware chain is mixing desk, 2 amps, and the Behringer?? or am I missing something.

Thanks again for your help

Before your amplifiers, by the way don't forget there's a lot of good used dear probably close to you

Cheers! Aside from the obvious ones like ebay do you have any recommendations for websites to find used gear in uk?

As said before the amps, these are not just crossovers, yes you will set your frequencies on them but they have parametric eq on all outputs, so tuning the system is fun, there is an online shop called " why-buy-new" they sell b-stock, scratches etc, you can get some really good deals on there.

Awesome! Thanks for your help!
I am still unsure which amps to choose bearing in mind I would need one to run both MHBs and one for the MT-130 but i am planning in future to build another 2 MHBs and another MT-130.

Peace!

www.thomann.de/gb/tamp_proline_3000.htm

ttp://www.thomann.de/gb/t-amp_ta2400.htm

These are exellent amps for the money, impessive guarantee, not to expensive.