You don't have to convert to unicode unless you need the language support.
I would probably echo that you are looking at replacing your hardware and you might want to assess if you want to back-end to AIX. Depending on your internal skillsets, cloud (outsourced) or switching to another architecture (Windows/SQL, etc) should be something to consider.
1. I would always convert to unicode. Every new installation comes with unicode - its only upgrades from pre-8.x that have the non-unicode support, so there would be less supported customers on non-unicode. Why go through an upgrade to end up having issues with support because you're not unicode ? Although it takes up more space on the database storage (~50%) - the penalty on performance would be also an issue, since a non-unicode database has to go through an extra "translation" process for every database transaction. So, make sure your consultant configures unicode when you're live in production.
2. Sticking with AIX is fine - again, this is bad advice - you likely have a large implementation and are looking for support across thousands of users and maybe you have other platforms that is hosted on AIX. AIX is a common implementation amongst E1 on Unix - though not as common these days as Linux or Solaris, since both are "native" oracle Unix products. However, you will likely have to re-consider your database platform - although UDB (10.5 or 9.7) is supported with EnterpriseOne - less than 1% of customers use UDB. Its an incredibly uncommon implementation choice, and I know that other customers have had issues getting support from Oracle over it. There have been a lot of rumors about Oracle dropping support for UDB in the past (which hasn't happened yet) - but it is the most logical platform that they would drop support for. You should consider going from UDB to Oracle (on Unix) - or getting an AS/400 and running DB2. Moving to Microsoft and SQL Server are definitely also another option - but if you don't have the skillset in house, then stick with what you have experience with. As far as scalability goes, all platforms are very scalable these days.
Lastly, don't forget that "8.0" is actually "B7334" - which is, for all intents and purposes, OneWorld Xe (its also called "Xe 2" in some CNC circles !). Its the most common upgrade process out there - but it is a big change, resulting in more than 750 table conversions that have to occur - and its very important to ensure that the partner you choose can not only help with your upgrade conversions, but also has experience in converting your data in a small enough window to minimize the impact of the go-live on your business.
Lastly, as for the cloud choice - don't get bamboozled. There are good companies that provide SAAS out there, and there are options to just host the hardware. Make sure you arm yourself with as much knowledge as possible - go to upgradejde.com to get all the technical information you can, and also ensure that Oracle is aware of the choices you're making. You might end up with an expensive licensing audit in the best case - or ending up paying substantially for a consulting organization to have "free reign" over your upgrade choices in the worst case. Do it right, and pick the partners that will serve YOU and not their pockets.