Where to go for overall integration...

I have encountered a problem and I don't know how to solve it. Also, I want to know what I think, what I have discussed in our company, and whether it is correct ....

My company is engaged in production and starts from small enterprises. Now it is a little large. In terms of information technology, the company used to be a small company and choose software from various aspects to achieve a single function. I believe many small enterprises share the same situation. Now, you need to connect software.

Discussed:

1. Should the functions of existing independent software be re-developed in ERP to reproduce the same functions? Or should we accept the broken similar functions in the existing ERP to achieve integration?
   for a specific business, we have a set of software specifically used to calculate the Product Quotation. After the quotation is made, we will make a product model for the guests and then receive the exact order, the order will be entered into the current ERP. In fact, there are quotation functions in ERP, but the functions cannot be compared with the software we purchased earlier. Similar situations also occur in different application links, not just quotation.
   switching another ERP system is impossible (to talk to some consultants about this problem, or to push R3 to me, or to Oracle or yonyou NC). Even if switching, it is impossible to find exactly what fits all our needs. ERP + 2 development, that is, the above mentioned, in the reproduction of an existing function, the cost and no significant value-added to the company.
   the internal discussion result is that you want to retain the old software. I think the results of this discussion are very reasonable. However, it is necessary to interact with the two sets of software. For example, the production cost of the model should be classified into the quotation. Or, in the future, when the customer has an order, the price should be taken from the quotation, the two must be consistent. In addition to being unable to interact, I hope there is another way to go. So the next question is how to connect ERP with the quotation system.
2. we already have six sets of software that require interaction. Do we need to develop them independently?
   I knew immediately that I could not write them separately. I don't want to modify or find someone to modify more than a dozen things in the future. I have learned this kind of maintenance nightmare before and don't want to happen again.
   after Google, almost all points to SOA. In my opinion, what I want is that the architecture is correct, but it does not need to be a web service. I'm not saying that so in SOA is equal to Web service, but we don't need web service. We have branch offices, but they do not have the right to buy software on their own, which is determined by the headquarters. Furthermore, our six sets of software, platforms, development languages, and database systems are all known. All are internal applications, all in the internal network. In the future, it will be too late to expose a service in the future. As for BPM, there is indeed a business logic in interaction.
   then, you can see the ESB.
   at present, I have no idea how to do this. Do you want to continue.

Aside from the question, my idea is that in the process of enterprise development, not many companies can throw 10 millions or 20 millions to launch Oracle, R3, and so on at the beginning. As a result, there must be different software in the process of growth, and it is normal for them to interact with each other. (Small and medium enterprises, such as us, do have a need for this. It seems that the value-added products do not provide practical functions.ProgramIt seems that no one wants to do this)

Speaking of this, there is no relationship between the integration solution and SOA, so we can achieve our goal. When looking for these middleware, we need to be flexible in the adjustment of business logic (such as the method similar to BPEL). reusability is a consideration, but there cannot be too much sacrifice.

It's hard to cook rice without rice, but it's hard to cook rice or make noodles? I just thought that I could not stop, and I had to find a solution if I was not budget enough. This may be a transitional period before purchasing a larger and better system.

I am looking for an answer in open source. Currently, I am studying JBoss + jbpm (which does not seem to be what I want), Apache camel, and the fusesource series.

I don't know much about it. I don't have any experience in these architectures, and I don't even know how to find it. Do you have any tips? Please notify me of the consultant's introduction to the above software ~

Thank you.