Can I beat up the 4.0 exhaust thing a little more?

I know this topic has been beet to death but as you can see i still need some help and just cant decide. I want to do this already. I know the muff will be flowmaster 40 delta....

I have a 99 xj 5.5 w/ 33's and not too many engine mods yet, K&N filter and going to put 2 2" holes in the stock box for now and eventually will work what i can. Need a few years before i have a stroker. For now with my near stock soon to be upgraded motor what should i do?.......

1) SIZE. something says go 2.5 just because i will get a header one day but for now don't want to be limited. Does the whole thing need to be the same size? if different what works best?
2) Down pipe. get rid of that dent and its cheap for a 2.25 but it seems if i go 2.5 there it must be custom made? whats a good price on that anyway?
3) Cat. High flow i guess ("high flow" isn't bull right?) and again size here?
4) Muff. i want the delta 40 wont mess with my system and sounds good. got that out of the way, except for size.
5) so tailpipe. i have a 2.25 w/ stainless tip (think dynomax and muff rusted out) this has some rust spots but still has some life and don't NEED to use it. otherwise its size?
6) welded and durability. I have done so many exhaust systems but never welded them. they never lasted for many years anyway. this time i think i should (between that and a possible custom down pipe i will need to go to a shop) would should they charge? also i don't want parts to rot one at a time and i cant change them if welded. Anyway to paint it and make it last?
$500-$600 would be great price but got little room. What do you all think

Save your money, don't spend $500-600 on an exhaust system. For a stockish motor there is little to no benefit to a lot of that.

Grab a decent muffler and cat (if the stock one is bad) and bank the other $300-400.

That said:
1) Stock is 2.25" after the muffler (2.5" in, 2.25" out). Really not going to gain anything changing it just to change it. If the muffler you get as a 2.5" out, use that instead but all you are doing is adding cost.
2) Don't worry about it. If it is really that bothersome any good muffler shop should be able to rid of it for you.
3) High flow really does mean high flow (as far as name brands go)
4) You figured it out, but not my personal choice.
5) Keep it. Then when you hit it on a rock or it really finally rusts through, replace it.
6) Welding it is not going to stop rot. It will help at the clamped connections (being that there will be none). Getting something other than the auto store cheap stuff will make it last longer. Aluminized and stainless work, but given the risk of damage in our applications it typically is not worth the cost.

1 APN header if it'll work on your year
2 hiflow cat from summit racing for cheap
3 whatever hiflow muffler/tailpipe you choose and call it done!