So for less than 1K for ALL of the audio mods you're looking for is tight but if it were me I would do the Match UP 7BMW and be done. You're not replacing any of the speakers at this point but you're addressing the poor factory amp with its factory canned sound processing. The Match UP 7BMW is plug and play, has 8 channel processing, has 7 channels of amplification (staggered power: 5x65 and 2x130)mounts onto the oem amplifier bracket, and includes center channel processing. Also, for that Match unit there are options for remotes, add on USB module (for high res USB), Bluetooth card/interface.
So if all you have is 1K max and won't spend any more then at this point you're done. But more importantly you laid the groundwork for future upgrades that make sense.
What I mean by groundwork and making sense having the Match unit first is that if you used your 1K budget for speakers first and left the factory amps as is then sure it would sound better than a fully stock audio system but you're still dealing with the limitations of the factory Amp which are factory set processing (set crossover frequencies and slopes, set EQ) and lack of power needed to provide dynamics. Also, if you replaced the processing and amplification first you can then source a much larger list of speakers that will work with your system compared to having to source plug and play type BMW speakers solutions like Eton and Bavsound. But more on that later.
So when you have more funds after acquiring the Match unit you can then start to replace speakers. Most important on the list are the front doors. Factory replacements like the Eton you mentioned get high praise on the forums. They are plug and play. They are still available, I did a quick google search and see they are at Madisound:
https://www.madisoundspeakerstore.co...00%20W-%20Pair
At this point your system will sound great and you may be happy enough to stop here. If you want more and have more funds, I (me in this situation) would look at changing the bass layout. Factory bass is handled by the under-seat 8" drivers. They are shallow drivers and lack sufficient xmax travel to reproduce sub bass frequencies as effectively as dedicated sub-bass drivers. I would add a 10" or 12" sub to the back trunk corner using a Musicar enclosure along with a mono amp to drive it. You could do a sub in a box but this would limit trunk space, choice is up to you. The sub will allow you to bandpass the underseat drivers to bridge the gap between the 4" door speakers and the sub. At this point you have gone from a 2 way to now having a 3 way front stage with a sub. More speakers handling the audio spectrum = better opportunity for better sound (depending on the drivers picked and your tuning skills)
After that, having more funds you can then improve your front stage further by then replacing the factory center channel drivers. (you only need 1x tweeter and 1x 4" driver with a crossover or a coaxial would work too. Preferably timber matching would require the same drivers as what you have in the doors, if you can source half a set somehow, or sell the other half? or go in with someone else who wants to upgrade their center channel?)
And after that with more available funds I would then replace the underseat 8" mid-bass drivers. Bavesound, Focal, Gladen, Jehnert and Eton make options.
Then, if you have more funds and think it could sound better, if you sourced a plug and play door speaker replacement like the Eton set mentioned above earlier I would then swap them out for a dedicated tweeter set and a dedicated 4" midrange driver set and would skip the passive crossover and have the DSP handle them with 4 channels now instead of two. 2 channels gained from not using the rear deck - keep reading.
And then with more money, the only factory speakers remaining are the rear deck speakers. I wouldn't put too much thought into these. Some or maybe a majority here would say to replace these early on but I would leave the factory ones alone and unplugged. Why? Because rear speakers pull the front stage away from in front of you where it should be. With proper DSP processing using time alignment, you can have rear fill to where it won't pull the front stage back. But I guess at this point you've spent a few thousand at least so what's another few hundred for a new rear fill speaker set. If you do then your 8 channel DSP can't handle 10 channels needed for this so your spending more for additional DSP or a separate DSP and/or separate amps.... rabbit hole.
Hope some other members with experience with the Match amp/DSP unit can chime in to offer their insight. Unfortunately, I am not taking this route. I already have invested in several amps and a few speakers leftover from a previous install I had in a previous car so I'll be doing separate amps and a separate DSP in my M240i when the time comes as I am still piecing it together but If I was going into this from scratch I would do the MATCH UP 7BMW in an instant and not have to do all the separate amps and a separate DSP. The MATCH unit just makes everything so easy.
TLDR;
For 1K just get the Match UP 7BMW and spend time learning how to tune. It will make the most improvement with just 1K max budget